Systems and methods for transmitting media content via digital radio broadcast transmission for synchronized rendering by a receiver

ABSTRACT

Systems, methods, and processor readable media are disclosed for encoding and transmitting first media content, second media content and triggering instructions to a digital radio broadcast receiver such that the triggering instructions arrive for immediate execution to trigger immediate rendering of the second media content in synchronization with the first media content.

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/385,660 filed Apr. 15, 2009, and claims the benefit of U.S.Provisional Application No. 61/272,580 filed Oct. 7, 2009, the entirecontents of each of which are incorporated herein by reference.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates to digital radio broadcast transmissionand reception of media content for synchronized rendering at a digitalradio broadcast receiver.

2. Background Information

Digital radio broadcasting technology delivers digital audio and dataservices to mobile, portable, and fixed receivers. One type of digitalradio broadcasting, referred to as in-band on-channel (IBOC) digitalaudio broadcasting (DAB), uses terrestrial transmitters in the existingMedium Frequency (MF) and Very High Frequency (VHF) radio bands. HDRadio™ Technology, developed by iBiquity Digital Corporation, is oneexample of an IBOC implementation for digital radio broadcasting andreception.

IBOC digital radio broadcasting signals can be transmitted in a hybridformat including an analog modulated carrier in combination with aplurality of digitally modulated carriers or in an all-digital formatwherein the analog modulated carrier is not used. Using the hybrid mode,broadcasters may continue to transmit analog AM and FM simultaneouslywith higher-quality and more robust digital signals, allowing themselvesand their listeners to convert from analog-to-digital radio whilemaintaining their current frequency allocations.

One feature of digital transmission systems is the inherent ability tosimultaneously transmit both digitized audio and data. Thus thetechnology also allows for wireless data services from AM and FM radiostations. The broadcast signals can include metadata, such as theartist, song title, or station call letters. Special messages aboutevents, traffic, and weather can also be included. For example, trafficinformation, weather forecasts, news, and sports scores can all bescrolled across a radio receiver's display while the user listens to aradio station.

IBOC digital radio broadcasting technology can provide digital qualityaudio, superior to existing analog broadcasting formats. Because eachIBOC digital radio broadcasting signal is transmitted within thespectral mask of an existing AM or FM channel allocation, it requires nonew spectral allocations. IBOC digital radio broadcasting promoteseconomy of spectrum while enabling broadcasters to supply digitalquality audio to the present base of listeners.

Multicasting, the ability to deliver several audio programs or servicesover one channel in the AM or FM spectrum, enables stations to broadcastmultiple services and supplemental programs on any of the sub-channelsof the main frequency. For example, multiple data services can includealternative music formats, local traffic, weather, news, and sports. Thesupplemental services and programs can be accessed in the same manner asthe traditional station frequency using tuning or seeking functions. Forexample, if the analog modulated signal is centered at 94.1 MHz, thesame broadcast in IBOC can include supplemental services 94.1-2, and94.1-3. Highly specialized supplemental programming can be delivered totightly targeted audiences, creating more opportunities for advertisersto integrate their brand with program content. As used herein,multicasting includes the transmission of one or more programs in asingle digital radio broadcasting channel or on a single digital radiobroadcasting signal. Multicast content can include a main programservice (MPS), supplemental program services (SPS), program service data(PSD), and/or other broadcast data.

The National Radio Systems Committee, a standard-setting organizationsponsored by the National Association of Broadcasters and the ConsumerElectronics Association, adopted an IBOC standard, designated NRSC-5, inSeptember 2005. NRSC-5 and its updates, the disclosure of which areincorporated herein by reference, set forth the requirements forbroadcasting digital audio and ancillary data over AM and FM broadcastchannels. The standard and its reference documents contain detailedexplanations of the RF/transmission subsystem and the transport andservice multiplex subsystems. Copies of the standard can be obtainedfrom the NRSC at http://www.nrscstandards.org/SG.asp. iBiquity's HDRadio technology is an implementation of the NRSC-5 IBOC standard.Further information regarding HD Radio technology can be found atwww.hdradio.com and www.ibiquity.com.

Other types of digital radio broadcasting systems include satellitesystems such as Satellite Digital Audio Radio Service (SDARS, e.g., XMRadio, Sirius), Digital Audio Radio Service (DARS, e.g., WorldSpace),and terrestrial systems such as Digital Radio Mondiale (DRM), Eureka 147(branded as DAB Digital Audio Broadcasting), DAB Version 2, and FMeXtra.As used herein, the phrase “digital radio broadcasting” encompassesdigital audio broadcasting including in-band on-channel broadcasting, aswell as other digital terrestrial broadcasting and satellitebroadcasting.

As described above, one advantage of digital radio broadcasting systemsis that they provide the capability to transmit multiple services,including audio and data, over one AM or FM frequency. For certainapplications, such as displaying album art, image slide shows, scrollingtext information, closed captioning, and product purchase information,it may be desirable to synchronize the content contained in one servicewith content contained in another service or to synchronize subservicesor components of the same service.

Conventional techniques known to the inventors for transmitting contentfor synchronized rendering by a receiver place responsibility andprocessing requirements for synchronization on the receiver. Forexample, the MPEG Transport System, which can be used to transmitsynchronized video content and audio content to be synchronized,includes a Program Clock Reference (PCR) 27 MHz clock signal in theTransport Stream for synchronization of the video and audio. Each videopacket and audio packet separately includes a Decode and PresentationTime Stamp referenced to the PCR that permit the receiver to determinewhen the packet should be decoded and rendered. As another example,Synchronized Media Integration Language v. 3.0 (SMIL) requires thereceiver to know the state of rendering primary content (e.g., how longan audio track has been playing) and provides attributes that mayspecify a begin time to render secondary content (e.g., album art) basedon the rendering of primary content, thus permitting the receiver todecode that information to provide proper synchronization. As anotherexample, SMIL also provides attributes that may specify a begin time torender secondary content at a predetermined universal coordinated time(UTC) regardless of the state of rendering the primary content.

However, the present inventors have found that none of these techniquesis entirely satisfactory for synchronizing content in the currentlydeployed HD Radio broadcast system. This system includes multiple andvarying signal processing paths on the transmit and, optionally, thereceive side that should be accounted for when synchronizing services orsubservices. In addition, digital radio broadcast receivers typicallyinclude a baseband processor that decodes the audio content and the datacontent and outputs audio to speakers. The data is then directed to ahost controller that processes and renders the data as media content.However, the host controller typically has no knowledge of the audiosamples, including the state of playback, since the audio is sentdirectly from the baseband processor to the speakers. The presentinventors have determined that conventional synchronization approachesare not helpful for such receiver configurations and use of conventionalapproaches would require undesirable modifications at the receiver side.

SUMMARY

Embodiments of the present disclosure are directed to systems andmethods that may satisfy these needs. According to exemplaryembodiments, a computer-implemented method is disclosed of encoding andtransmitting first media content, second media content and triggeringinstructions to a digital radio broadcast receiver such that thetriggering instructions arrive for immediate execution to triggerimmediate rendering of the second media content in synchronization withthe first media content. The method comprises determining at theprocessing system a first value corresponding to a time at which a frameincluding first media content is to be transmitted by a digital radiobroadcast transmitter; determining at the processing system a secondvalue corresponding to a time at which first media content transmittedin the frame is to be rendered by a digital radio broadcast receiverbased on a first latency, wherein the first latency is based on anestimated time for processing the first media content via a first signalpath through the digital radio broadcast transmitter; determining at theprocessing system a third value corresponding to a time at which secondmedia content would be rendered by the digital radio broadcast receiverbased on a second latency, wherein the second latency is based on anestimated time for processing the second media content via a secondsignal path through the digital radio broadcast transmitter, and whereinthe second latency is different than the first latency; determining atthe processing system a channel data capacity for broadcasting thesecond media content via digital radio broadcast transmission;processing the second media content at the processing system based onthe first value, second value, third value and the channel data capacityto determine a time at which second media content is to be transmittedto the digital radio broadcast receiver, so as to as to be received at adigital broadcast radio receiver for rendering in synchronization withthe first media content at the digital radio broadcast receiver;generating triggering instructions based on the first value, secondvalue, third value and the channel data capacity to trigger therendering of the second media content in synchronization with the firstmedia content at the digital radio broadcast receiver, such that thetriggering instructions arrive at the digital radio broadcast receiverfor immediate execution to trigger immediate rendering of the secondmedia content in synchronization with the first media content; andcommunicating to the digital radio broadcast transmitter, the firstvalue, first media content, second media content, and the triggeringinstructions.

In another embodiment, a computer-implemented method is disclosed forprocessing first media content, second media content and triggeringinstructions received via digital radio broadcast transmission such thatthe triggering instructions arrive for immediate execution to triggerimmediate rendering of the second media content in synchronization withthe first media content. The method comprises receiving first mediacontent and second media content; receiving triggering instructions tocause the second media content to be rendered by a digital radiobroadcast receiver based on the time at which the first media contentwill be rendered, wherein the triggering instructions are scheduled soas to arrive at the digital radio broadcast receiver for immediateexecution to trigger immediate rendering of the second media content insynchronization with the first media content; determining whether acommercial frame having a promotional message associated with the secondmedia content has been received; and if the commercial frame having thepromotional message associated with the second media content has notbeen received, refraining from rendering the second media content.

In another embodiment, a computer-implemented method is disclosed forprocessing first media content, second media content and triggeringinstructions for broadcast to a digital radio broadcast receiver viadigital radio broadcast transmission such that the triggeringinstructions arrive for immediate execution to trigger immediaterendering of the second media content in synchronization with the firstmedia content. The method comprises determining a time at which a firstmedia content will be rendered at a digital radio broadcast receiver;generating triggering instructions to cause a second media content to berendered by a digital radio broadcast receiver based on the time atwhich the first media content will be rendered, wherein the triggeringinstructions are scheduled so as to arrive at the digital radiobroadcast receiver for immediate execution to trigger immediaterendering of the second media content in synchronization with the firstmedia content; processing broadcast frames including the first mediacontent and the triggering instructions for broadcast via digital radiobroadcast transmission; determining whether a commercial frame having apromotional message associated with the second media content has beengenerated; and if the commercial frame has been generated, processingthe second media content and the commercial frame for broadcast viadigital radio broadcast transmission, the commercial frame being timedfor rendering at the digital radio broadcast receiver along with thefirst media content and the second media content.

A system comprising a processing system and a memory coupled to theprocessing system is described wherein the processing system isconfigured to carry out the above-described methods. Computerprogramming instructions adapted to cause a processing system to carryout the above-described methods may be embodied within any suitablearticle of manufacture such as a computer readable storage medium.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescription, appended claims, and accompanying drawings wherein:

FIG. 1 illustrates a block diagram that provides an overview of a systemin accordance with certain embodiments;

FIG. 2 is a schematic representation of a hybrid FM IBOC waveform;

FIG. 3 is a schematic representation of an extended hybrid FM IBOCwaveform;

FIG. 4 is a schematic representation of an all-digital FM IBOC waveform;

FIG. 5 is a schematic representation of a hybrid AM IBOC waveform;

FIG. 6 is a schematic representation of an all-digital AM IBOC waveform;

FIG. 7 is a functional block diagram of an AM IBOC digital radiobroadcasting receiver in accordance with certain embodiments;

FIG. 8 is a functional block diagram of an FM IBOC digital radiobroadcasting receiver in accordance with certain embodiments;

FIGS. 9 a and 9 b are diagrams of an IBOC digital radio broadcastinglogical protocol stack from the broadcast perspective;

FIG. 10 is a diagram of an IBOC digital radio broadcasting logicalprotocol stack from the receiver perspective;

FIG. 11 is a functional block diagram of digital radio broadcasttransmitter components in accordance with certain embodiments;

FIG. 12 is an exemplary timeline illustrating determining a time tobegin transferring a media content file such that it is available forrendering in synchronization with an audio track at a digital radiobroadcast receiver in accordance with certain embodiments;

FIG. 13 is an exemplary signal diagram for creating a modem frame inaccordance with certain embodiments;

FIG. 14 is an exemplary data control service in accordance with certainembodiments;

FIG. 15 illustrates an exemplary chart showing ID3 tag size versus PSDdelay for MPS audio in accordance with certain embodiments;

FIG. 16 illustrates an exemplary chart showing ID3 tag size versus PSDdelay for SPS audio in accordance with certain embodiments;

FIG. 17 illustrates an exemplary ID3 tag in accordance with certainembodiments;

FIG. 18 illustrates an exemplary content protocol in accordance withcertain embodiments;

FIGS. 19 a to 19 d illustrate exemplary album art synchronizationapplications in accordance with certain embodiments;

FIG. 20 illustrates an exemplary operation of an image renderingapplication in accordance with certain embodiments;

FIGS. 21 a and 21 b illustrate an exemplary digital radio receiver vocalreducing and/or eliminating capability for radio karaoke in accordancewith certain embodiments;

FIG. 22 illustrates an exemplary process of generating synchronizedmedia content in a digital radio broadcast transmitter system fordigital radio broadcast in accordance with certain embodiments; and

FIG. 23 illustrates an exemplary process of receiving and renderingsynchronized media content in a digital radio broadcast receiver inaccordance with certain embodiments.

DESCRIPTION

Digital radio broadcast systems as described herein can transmit mediacontent for synchronized rendering at a digital radio broadcastreceiver. To overcome the receiver intensive processing required forconventional synchronization techniques, the present inventors havedeveloped novel processing of media content at the transmitter side sothat different media content can be rendered in synchronization at thereceiver.

An advantage that the approaches disclosed herein may provide is thatthe triggering instructions for rendering second media content (e.g.,album art) are closely coupled to the associated audio content by virtueof the triggering instructions being contained in the program servicedata (PSD). PSD is tightly aligned with its associated audio content andexemplary embodiments of the present invention may take advantage ofthis characteristic to easily and efficiently send triggeringinformation. Moreover, existing receivers are already capable ofprocessing PSD information, making the techniques of the presentinvention backward compatible. As an additional advantage, images mayoptionally be stored by the receiver for only a short amount of time,thereby reducing the overall storage capacity needed for the secondmedia content.

Exemplary Digital Radio Broadcasting System

FIGS. 1-10 and the accompanying description herein provide a generaldescription of an exemplary IBOC system, exemplary broadcastingequipment structure and operation, and exemplary receiver structure andoperation. FIGS. 11-22 and the accompanying description herein provide adetailed description of exemplary approaches for transmitting mediacontent for synchronized rendering in a digital radio broadcast systemin accordance with exemplary embodiments of the present disclosure.Whereas aspects of the disclosure are presented in the context of anexemplary IBOC system, it should be understood that the presentdisclosure is not limited to IBOC systems and that the teachings hereinare applicable to other forms of digital radio broadcasting as well.

As referred to herein, a service is any analog or digital medium forcommunicating content via radio frequency broadcast. For example, in anIBOC radio signal, the analog modulated signal, the digital main programservice, and the digital supplemental program services could all beconsidered services. Other examples of services can includeconditionally accessed programs (CAs), which are programs that require aspecific access code and can be both audio and/or data such as, forexample, a broadcast of a game, concert, or traffic update service, anddata services, such as traffic data, multimedia and other files, andservice information guides (SIGs).

Additionally, as referred to herein, media content is any substantiveinformation or creative material, including, for example, audio, video,text, image, or metadata, that is suitable for processing by aprocessing system to be rendered, displayed, played back, and/or used bya human.

Furthermore, one of ordinary skill in the art would appreciate that whatamounts to synchronization can depend on the particular implementation.As a general matter, two pieces of content are synchronized if they makesense in temporal relation to one another when rendered to a listener.For example, album art may be considered synchronized with associatedaudio if the onset of the images either leads or follows the onset ofthe audio by 3 seconds or less. For a karaoke implementation, forexample, a word of karaoke text should not follow its associated timefor singing that word but can be synchronized if it precedes the timefor singing the word by as much as a few seconds (e.g., 1 to 3 seconds).In other embodiments, content may be deemed synchronized if it isrendered, for example, within about +/−3 seconds of associated audio, orwithin about +/− one-tenth of a second of associated audio.

Referring to the drawings, FIG. 1 is a functional block diagram ofexemplary relevant components of a studio site 10, an FM transmittersite 12, and a studio transmitter link (STL) 14 that can be used tobroadcast an FM IBOC digital radio broadcasting signal. The studio siteincludes, among other things, studio automation equipment 34, anEnsemble Operations Center (EOC) 16 that includes an importer 18, anexporter 20, and an exciter auxiliary service unit (EASU) 22. An STLtransmitter 48 links the EOC with the transmitter site. The transmittersite includes an STL receiver 54, an exciter 56 that includes an exciterengine (exgine) subsystem 58, and an analog exciter 60. While in FIG. 1the exporter is resident at a radio station's studio site and theexciter is located at the transmission site, these elements may beco-located at the transmission site.

At the studio site, the studio automation equipment supplies mainprogram service (MPS) audio 42 to the EASU, MPS data 40 to the exporter,supplemental program service (SPS) audio 38 to the importer, and SPSdata 36 to the importer 18. MPS audio serves as the main audioprogramming source. In hybrid modes, it preserves the existing analogradio programming formats in both the analog and digital transmissions.MPS data or SPS data, also known as program service data (PSD), includesinformation such as music title, artist, album name, etc. PSD istypically encoded using ID3 tags. Supplemental program service caninclude supplementary audio content as well as program service data.

The importer 18 contains hardware and software for supplying advancedapplication services (AAS). AAS can include any type of data that is notclassified as MPS, SPS, or Station Information Service (SIS). SISprovides station information, such as call sign, absolute time, positioncorrelated to GPS, etc. Examples of AAS include data services forelectronic program guides, navigation maps, real-time traffic andweather information, multimedia applications, other audio services, andother data content. The content for AAS can be supplied by serviceproviders 44, which provide service data 46 to the importer via anapplication program interface (API). The service providers may be abroadcaster located at the studio site or externally sourced third-partyproviders of services and content. The importer can establish sessionconnections between multiple service providers. The importer encodes andmultiplexes service data 46, SPS audio 38, and SPS data 36 to produceexporter link data 24, which is output to the exporter via a data link.The importer 18 also encodes a SIG, in which it typically identifies anddescribes available services. For example, the SIG may include dataidentifying the genre of the services available on the current frequency(e.g., the genre of MPS audio and any SPS audio).

The importer 18 can use a data transport mechanism, which may bereferred to herein as a radio link subsystem (RLS), to provide packetencapsulation, varying levels of quality of service (e.g., varyingdegrees of forward error correction and interleaving), and bandwidthmanagement functions. The RLS uses High-Level Data Link Control (HDLC)type framing for encapsulating the packets. HDLC is known to one ofskill in the art and is described in ISO/IEC 13239:2002 Informationtechnology—Telecommunications and information exchange betweensystems—High-level data link control (HDLC) procedures. HDLC framingincludes a beginning frame delimiter (e.g., ‘0x7E’) and an ending framedelimiter (e.g., ‘0x7E’). The RLS header includes a logical address(e.g., port number), a control field for sequence numbers and otherinformation (e.g., packet 1 of 2, 2 of 2 etc.), the payload (e.g., theindex file), and a checksum (e.g., a CRC). For bandwidth management, theimporter 18 typically assigns logical addresses (e.g. ports) to AAS databased on, for example, the number and type of services being configuredat any given studio site 10. RLS is described in more detail in U.S.Pat. No. 7,305,043, which is incorporated herein by reference in itsentirety.

In media content transmission applications, the amount of bandwidth theimporter 18 allocates to a given service depends upon several factorsincluding: a) the size of the media content (e.g., the image or videosize); b) the amount of time the media content is retransmitted forerror mitigation; and c) the rate at which the media content needs toarrive, or alternatively, how long the media content should bedisplayed.

The size of the media content (e.g., images) depends upon the number ofpixels, the amount and type of compression used, and the complexity ofthe original image. Images transmitted for use as cover art or stationlogos typically have the following characteristics: a) image resolutionwithin 170-200×170-200 pixels; b) square images are preferable; c)gray-scale or color are possible; d) gray-scale images are typically8-bits per pixel; f) color images are typically 24-bits per pixel(8-bits each for red, green and blue); and g) file sizes typically have24 kbyte maximum size, with 12 kbyte nominal. Other applications willhave image characteristics suitable for the given application.

In exemplary embodiments, it may be desirable to retransmit mediacontent such as images to improve robustness to channel errors. Thenumber of times media content is retransmitted is an implementationdecision that relates to the reliability of the communication channel.As such, various repeat strategies may be used with media content files.For example, one strategy that may be desirable when transmitting albumart images is that the first transmission of each image is sent prior tothe start of an associated audio track, and sending a second occurrenceof the image file immediately after the start of the song. If there areno errors in the received file, the image will be rendered by thereceiver coincident with the beginning of the track. And if the receiverfailed to receive the image after the first transmission, it can quicklyrecover the image on the second occurrence while the song is still inprogress. In another example, if the broadcaster has sufficientbandwidth each album art image may be transmitted three times. In thiscase, each image is sent twice prior to the beginning of the audiotrack, and once after the start of the track (for fast receiveracquisition). Each image file is interleaved with others to increase thelikelihood of the receiver recovering the image in the presence of bursterrors (e.g., long signal dropouts) on the RF channel.

The number of retransmissions is a design choice involving a tradeoffbetween bandwidth requirements and reliability. For example, assume apacket size of 256 bytes and a conservative estimate of 1% packet losson the communication channel. The typical image and file sizes describedabove will require 12, 50, and 100 256-byte packets to transmit 3 kbyte,12.5 kbyte, and 24 kbyte files respectively. Assuming uniformlydistributed packet errors, the probability of receiving an entire imagefile would then be approximated as: P=1−(0.99)^(N); where N=15, 50, or100. Table 1 below shows the result of these approximations forrepeating transmission of the image 1, 2, and 3 times.

TABLE 1 File size Number of Times a File is Transmitted (kbytes) 1 2 3 388% 98% 99.9%   12.5 60% 84% 93% 24 26% 59% 73%Based on these approximations, a value of 2 transmissions may yield anacceptable trade-off. Obviously, any value of transmissions can beused—increasing the number of transmissions will increase reliabilityand bandwidth usage, and decreasing the number of transmissions willreduce reliability and bandwidth usage.

The time between displaying different media content files is the thirdparameter when allocating bandwidth. This time is a function of theapplication. For example, in cover art applications if only one image isdisplayed per song, then the transfer time can be on the order of twominutes, whereas if the application is a slide show or if images need tobe displayed with advertisements, a new image could be needed every 15seconds. Typically, the shortest time between image displays should beused to calculate bandwidth requirements. As an illustration, assume aslide show displays 300×300 pixel images once every 15 seconds (˜10ALFNs) using a repeat value of 2. Then T_(T) (Transmit time)=10 ALFNs(˜15 seconds) with 1 PDU per ALFN, and S_(I) (Size of the image)=48kbytes (2×24 kbytes). Thus B (required bandwidth)=S_(I)/T_(T)=48kbytes/10 PDUs=4.8 kbytes per PDU, which is approximately 25 kbit/s.

Due to receiver implementation choices, RLS packets can be limited insize to about 8192 bytes, but other sizes could be used. Therefore, inexemplary embodiments data may be prepared for transmission according tofour data segmentation modes—standard packets, variable packets, largeobject transfer (LOT), and byte-streaming—for transmitting objectslarger than the maximum packet size.

In packet delivery mode (i.e., standard and variable packet modes),packets are delivered to the importer 18 already encapsulated by aclient application. In standard packet mode, the client application islimited to packet sizes no greater than its bandwidth allocation on aper PDU basis. Therefore the client application should have knowledge ofits allocated bandwidth (bit/s) and the rate of the logical channelbeing used to broadcast data. For example, the P1 logical channel has aPDU rate of approximately 1.486 seconds and the P3 logical channel has aPDU rate of approximately 0.186 seconds. Based on these characteristics,a client application with a bandwidth allocation using P1 of 1 kbit/secwould be limited in packet size to (1000 bits/sec)×(1 byte/8bits)×(1.486 seconds per PDU)=185 bytes. An advantage of standard packetmode is that packets are guaranteed to be delivered to the receiver inevery PDU. Therefore, if the client application can adjust its nativepacket size to match its bandwidth allocation and logical channel rate,it can use native encapsulation to minimize processing on the receiverside.

Variable packet mode is similar to standard packet mode except that thepacket sizes are independent of the allocated bandwidth. This means thatthe bandwidth allocation is statistical in nature and clientapplications may incur substantial jitter in the delivery of the datapackets (i.e., there is a non-guaranteed delivery time). However, theadvantage of variable packets is that the importer can allocate minimalbandwidth to the service and still maintain their native packetstructure independent of the logical channel. On the other hand,services that are allocated minimal bandwidth will affect the deliveryjitter of all other data services using variable packet mode (i.e.,services do not control their own performance). Thus, the variablepacket mode is best suited for non-real time applications. Whentransmitting images, the difference between the packet delivery methodscan affect how far in advance the image must be transmitted to ensurethat it arrives in time to be rendered in synchronization with theassociated audio.

The importer 18 may also include a large object transfer (LOT) client(e.g. a software client that executes on the same computer processingsystem as the importer 18 or on a different processing system such as aremote processing system) to segment a “large” object (for example, asizeable image file) into fragments no larger than the chosen RLS packetsize. In typical embodiments objects may range in size up to4,294,967,295 bytes. At the transmitter, the LOT client writes packetsto an RLS port for broadcast to the receiver. At the receiver, the LOTclient reads packets from the RLS port of the same number. The LOTclient may process data associated with many RLS ports (e.g., typicallyup to 32 ports) simultaneously, both at the receiver and thetransmitter.

The LOT client operates by sending a large object in several messages,each of which is no longer than the maximum packet size. To accomplishthis, the transmitter assigns an integer called a LOTID to each objectbroadcast via the LOT protocol. All messages for the same object willuse the same LOTID. The choice of LOTID is arbitrary except that no twoobjects being broadcast concurrently on the same RLS port may have thesame LOTID. In some implementations, it may be advantageous to exhaustall possible LOTID values before a value is reused.

When transmitting data over-the-air, there may be some packet loss dueto the probabilistic nature of the radio propagation environment. TheLOT client addresses this issue by allowing the transmitter to repeatthe transmission of an entire object. Once an object has been receivedcorrectly, the receiver can ignore any remaining repetitions. Allrepetitions will use the same LOTID. Additionally, the transmitter mayinterleave messages for different objects on the same RLS port so longas each object on the port has been assigned a unique LOTID.

The LOT client divides a large object into messages, which are furthersubdivided into fragments. Preferably all the fragments in a message,excepting the last fragment, are a fixed length such as 256 bytes. Thelast fragment may be any length that is less than the fixed length(e.g., less than 256 bytes). Fragments are numbered consecutivelystarting from zero. However, in some embodiments an object may have azero-length object—the messages would contain only descriptiveinformation about the object.

The LOT client typically uses two types of messages—a full headermessage, and a fragment header message. Each message includes a headerfollowed by fragments of the object. The full header message containsthe information to reassemble the object from the fragments plusdescriptive information about the object. By comparison, the fragmentheader message contains only the reassembly information. The LOT clientof the receiver (e.g. a software and/or hardware application thattypically executes within the data processors 232 and 288 of FIGS. 7 and8 respectively or any other suitable processing system) distinguishesbetween the two types of messages by a header-length field (e.g. fieldname “hdrLen”). Each message can contain any suitable number offragments of the object identified by the LOTID in the header as long asthe maximum RLS packet length is not exceeded. There is no requirementthat all messages for an object contain the same number of fragments.Table 2 below illustrates exemplary field names and their correspondingdescriptions for a full header message. Fragment header messagestypically include only the hdrLen, repeat, LOTID, and position fields.

TABLE 2 FIELD NAME FIELD DESCRIPTION hdrLen Size of the header in bytes,including the hdrLen field. Typically ranges from 24-255 bytes. RepeatNumber of object repetitions remaining. Typically ranges from 0 to 255.All messages for the same repetition of the object use the same repeatvalue. When repeating an object, the transmitter broadcasts all messageshaving repeat = R before broadcasting any messages having repeat = R− 1. A value of 0 typically means the object will not be repeated again.LOTID Arbitrary identifier assigned by the transmitter to the object.Typically range from 0 to 65,535. All messages for the same object usethe same LOTID value. Position The byte offset in the reassembled objectof the first fragment in the message equals 256*position. Equivalent to“fragment number”. Version Version of the LOT protocol discardTime Year,month, day, hour, and minute after which the object may be discarded atthe receiver. Expressed in Coordinated Universal Time (UTC). fileSizeTotal size of the object in bytes. mime Hash MIME hash describing thetype of object filename File name associated with the object

Full header and fragment header messages may be sent in any ratioprovided that at least one full header message is broadcast for eachobject. Bandwidth efficiency will typically be increased by minimizingthe number of full header messages; however, this may increase the timenecessary for the receiver to determine whether an object is of interestbased on the descriptive information that is only present in the fullheader. Therefore there is typically a trade between efficient use ofbroadcast bandwidth and efficient receiver processing and reception ofdesired LOT files.

In byte-streaming mode, as in packet mode, each data service isallocated a specific bandwidth by the radio station operators based onthe limits of the digital radio broadcast modem frames. The importer 18then receives data messages of arbitrary size from the data services.The data bytes received from each service are then placed in a bytebucket (e.g. a queue) and HDLC frames are constructed based on thebandwidth allocated to each service. For example, each service may haveits own HDLC frame that will be just the right size to fit into a modemframe. For example, assume that there are two data services, service #1and service #2. Service #1 has been allocated 1024 bytes, and service #2512 bytes. Now assume that service #1 sends message A having 2048 bytes,and service #2 sends message B also having 2048 bytes. Thus the firstmodem frame will contain two HDLC frames; a 1024 byte frame containing Nbytes of message A and a 512 byte HDLC frame containing M bytes ofmessage B. N & M are determined by how many HDLC escape characters areneeded and the size of the RLS header information. If no escapecharacters are needed then N=1015 and M=503 assuming a 9 byte RLSheader. If the messages contain nothing but HDLC framing bytes (i.e.0x7E) then N=503 and M=247, again assuming a 9 byte RLS headercontaining no escape characters. Also, if data service #1 does not senda new message (call it message AA) then its unused bandwidth may begiven to service #2 so its HDLC frame will be larger than its allocatedbandwidth of 512 bytes.

The exporter 20 contains the hardware and software necessary to supplythe main program service and SIS for broadcasting. The exporter acceptsdigital MPS audio 26 over an audio interface and compresses the audio.The exporter also multiplexes MPS data 40, exporter link data 24, andthe compressed digital MPS audio to produce exciter link data 52. Inaddition, the exporter accepts analog MPS audio 28 over its audiointerface and applies a pre-programmed delay to it to produce a delayedanalog MPS audio signal 30. This analog audio can be broadcast as abackup channel for hybrid IBOC digital radio broadcasts. The delaycompensates for the system delay of the digital MPS audio, allowingreceivers to blend between the digital and analog program without ashift in time. In an AM transmission system, the delayed MPS audiosignal 30 is converted by the exporter to a mono signal and sentdirectly to the STL as part of the exciter link data 52.

The EASU 22 accepts MPS audio 42 from the studio automation equipment,rate converts it to the proper system clock, and outputs two copies ofthe signal, one digital (26) and one analog (28). The EASU includes aGPS receiver that is connected to an antenna 25. The GPS receiver allowsthe EASU to derive a master clock signal, which is synchronized to theexciter's clock by use of GPS units. The EASU provides the master systemclock used by the exporter. The EASU is also used to bypass (orredirect) the analog MPS audio from being passed through the exporter inthe event the exporter has a catastrophic fault and is no longeroperational. The bypassed audio 32 can be fed directly into the STLtransmitter, eliminating a dead-air event.

STL transmitter 48 receives delayed analog MPS audio 50 and exciter linkdata 52. It outputs exciter link data and delayed analog MPS audio overSTL link 14, which may be either unidirectional or bidirectional. TheSTL link may be a digital microwave or Ethernet link, for example, andmay use the standard User Datagram Protocol or the standard TCP/IP.

The transmitter site includes an STL receiver 54, an exciter engine(exgine) 56 and an analog exciter 60. The STL receiver 54 receivesexciter link data, including audio and data signals as well as commandand control messages, over the STL link 14. The exciter link data ispassed to the exciter 56, which produces the IBOC digital radiobroadcasting waveform. The exciter includes a host processor, digitalup-converter, RF up-converter, and exgine subsystem 58. The exgineaccepts exciter link data and modulates the digital portion of the IBOCdigital radio broadcasting waveform. The digital up-converter of exciter56 converts from digital-to-analog the baseband portion of the exgineoutput. The digital-to-analog conversion is based on a GPS clock, commonto that of the exporter's GPS-based clock derived from the EASU. Thus,the exciter 56 includes a GPS unit and antenna 57. An alternative methodfor synchronizing the exporter and exciter clocks can be found in U.S.Pat. No. 7,512,175, the disclosure of which is hereby incorporated byreference. The RF up-converter of the exciter up-converts the analogsignal to the proper in-band channel frequency. The up-converted signalis then passed to the high power amplifier 62 and antenna 64 forbroadcast. In an AM transmission system, the exgine subsystem coherentlyadds the backup analog MPS audio to the digital waveform in the hybridmode; thus, the AM transmission system does not include the analogexciter 60. In addition, in an AM transmission system, the exciter 56produces phase and magnitude information and the analog signal is outputdirectly to the high power amplifier.

IBOC digital radio broadcasting signals can be transmitted in both AMand FM radio bands, using a variety of waveforms. The waveforms includean FM hybrid IBOC digital radio broadcasting waveform, an FM all-digitalIBOC digital radio broadcasting waveform, an AM hybrid IBOC digitalradio broadcasting waveform, and an AM all-digital IBOC digital radiobroadcasting waveform.

FIG. 2 is a schematic representation of a hybrid FM IBOC waveform 70.The waveform includes an analog modulated signal 72 located in thecenter of a broadcast channel 74, a first plurality of evenly spacedorthogonally frequency division multiplexed subcarriers 76 in an uppersideband 78, and a second plurality of evenly spaced orthogonallyfrequency division multiplexed subcarriers 80 in a lower sideband 82.The digitally modulated subcarriers are divided into partitions andvarious subcarriers are designated as reference subcarriers. A frequencypartition is a group of 19 OFDM subcarriers containing 18 datasubcarriers and one reference subcarrier.

The hybrid waveform includes an analog FM-modulated signal, plusdigitally modulated primary main subcarriers. The subcarriers arelocated at evenly spaced frequency locations. The subcarrier locationsare numbered from −546 to +546. In the waveform of FIG. 2, thesubcarriers are at locations +356 to +546 and −356 to −546. Each primarymain sideband is comprised of ten frequency partitions. Subcarriers 546and −546, also included in the primary main sidebands, are additionalreference subcarriers. The amplitude of each subcarrier can be scaled byan amplitude scale factor.

FIG. 3 is a schematic representation of an extended hybrid FM IBOCwaveform 90. The extended hybrid waveform is created by adding primaryextended sidebands 92, 94 to the primary main sidebands present in thehybrid waveform. One, two, or four frequency partitions can be added tothe inner edge of each primary main sideband. The extended hybridwaveform includes the analog FM signal plus digitally modulated primarymain subcarriers (subcarriers +356 to +546 and −356 to −546) and some orall primary extended subcarriers (subcarriers +280 to +355 and −280 to−355).

The upper primary extended sidebands include subcarriers 337 through 355(one frequency partition), 318 through 355 (two frequency partitions),or 280 through 355 (four frequency partitions). The lower primaryextended sidebands include subcarriers −337 through −355 (one frequencypartition), −318 through −355 (two frequency partitions), or −280through −355 (four frequency partitions). The amplitude of eachsubcarrier can be scaled by an amplitude scale factor.

FIG. 4 is a schematic representation of an all-digital FM IBOC waveform100. The all-digital waveform is constructed by disabling the analogsignal, fully extending the bandwidth of the primary digital sidebands102, 104, and adding lower-power secondary sidebands 106, 108 in thespectrum vacated by the analog signal. The all-digital waveform in theillustrated embodiment includes digitally modulated subcarriers atsubcarrier locations −546 to +546, without an analog FM signal.

In addition to the ten main frequency partitions, all four extendedfrequency partitions are present in each primary sideband of theall-digital waveform. Each secondary sideband also has ten secondarymain (SM) and four secondary extended (SX) frequency partitions. Unlikethe primary sidebands, however, the secondary main frequency partitionsare mapped nearer to the channel center with the extended frequencypartitions farther from the center.

Each secondary sideband also supports a small secondary protected (SP)region 110, 112 including 12 OFDM subcarriers and reference subcarriers279 and −279. The sidebands are referred to as “protected” because theyare located in the area of spectrum least likely to be affected byanalog or digital interference. An additional reference subcarrier isplaced at the center of the channel (0). Frequency partition ordering ofthe SP region does not apply since the SP region does not containfrequency partitions.

Each secondary main sideband spans subcarriers 1 through 190 or −1through −190. The upper secondary extended sideband includes subcarriers191 through 266, and the upper secondary protected sideband includessubcarriers 267 through 278, plus additional reference subcarrier 279.The lower secondary extended sideband includes subcarriers −191 through−266, and the lower secondary protected sideband includes subcarriers−267 through −278, plus additional reference subcarrier −279. The totalfrequency span of the entire all-digital spectrum is 396,803 Hz. Theamplitude of each subcarrier can be scaled by an amplitude scale factor.The secondary sideband amplitude scale factors can be user selectable.Any one of the four may be selected for application to the secondarysidebands.

In each of the waveforms, the digital signal is modulated usingorthogonal frequency division multiplexing (OFDM). OFDM is a parallelmodulation scheme in which the data stream modulates a large number oforthogonal subcarriers, which are transmitted simultaneously. OFDM isinherently flexible, readily allowing the mapping of logical channels todifferent groups of subcarriers.

In the hybrid waveform, the digital signal is transmitted in primarymain (PM) sidebands on either side of the analog FM signal in the hybridwaveform. The power level of each sideband is appreciably below thetotal power in the analog FM signal. The analog signal may be monophonicor stereophonic, and may include subsidiary communications authorization(SCA) channels.

In the extended hybrid waveform, the bandwidth of the hybrid sidebandscan be extended toward the analog FM signal to increase digitalcapacity. This additional spectrum, allocated to the inner edge of eachprimary main sideband, is termed the primary extended (PX) sideband.

In the all-digital waveform, the analog signal is removed and thebandwidth of the primary digital sidebands is fully extended as in theextended hybrid waveform. In addition, this waveform allows lower-powerdigital secondary sidebands to be transmitted in the spectrum vacated bythe analog FM signal.

FIG. 5 is a schematic representation of an AM hybrid IBOC digital radiobroadcasting waveform 120. The hybrid format includes the conventionalAM analog signal 122 (bandlimited to about ±5 kHz) along with a nearly30 kHz wide digital radio broadcasting signal 124. The spectrum iscontained within a channel 126 having a bandwidth of about 30 kHz. Thechannel is divided into upper 130 and lower 132 frequency bands. Theupper band extends from the center frequency of the channel to about +15kHz from the center frequency. The lower band extends from the centerfrequency to about −15 kHz from the center frequency.

The AM hybrid IBOC digital radio broadcasting signal format in oneexample comprises the analog modulated carrier signal 134 plus OFDMsubcarrier locations spanning the upper and lower bands. Coded digitalinformation representative of the audio or data signals to betransmitted (program material), is transmitted on the subcarriers. Thesymbol rate is less than the subcarrier spacing due to a guard timebetween symbols.

As shown in FIG. 5, the upper band is divided into a primary section136, a secondary section 138, and a tertiary section 144. The lower bandis divided into a primary section 140, a secondary section 142, and atertiary section 143. For the purpose of this explanation, the tertiarysections 143 and 144 can be considered to include a plurality of groupsof subcarriers labeled 146 and 152 in FIG. 5. Subcarriers within thetertiary sections that are positioned near the center of the channel arereferred to as inner subcarriers, and subcarriers within the tertiarysections that are positioned farther from the center of the channel arereferred to as outer subcarriers. The groups of subcarriers 146 and 152in the tertiary sections have substantially constant power levels. FIG.5 also shows two reference subcarriers 154 and 156 for system control,whose levels are fixed at a value that is different from the othersidebands.

The power of subcarriers in the digital sidebands is significantly belowthe total power in the analog AM signal. The level of each OFDMsubcarrier within a given primary or secondary section is fixed at aconstant value. Primary or secondary sections may be scaled relative toeach other. In addition, status and control information is transmittedon reference subcarriers located on either side of the main carrier. Aseparate logical channel, such as an IBOC Data Service (IDS) channel canbe transmitted in individual subcarriers just above and below thefrequency edges of the upper and lower secondary sidebands. The powerlevel of each primary OFDM subcarrier is fixed relative to theunmodulated main analog carrier. However, the power level of thesecondary subcarriers, logical channel subcarriers, and tertiarysubcarriers is adjustable.

Using the modulation format of FIG. 5, the analog modulated carrier andthe digitally modulated subcarriers are transmitted within the channelmask specified for standard AM broadcasting in the United States. Thehybrid system uses the analog AM signal for tuning and backup.

FIG. 6 is a schematic representation of the subcarrier assignments foran all-digital AM IBOC digital radio broadcasting waveform. Theall-digital AM IBOC digital radio broadcasting signal 160 includes firstand second groups 162 and 164 of evenly spaced subcarriers, referred toas the primary subcarriers, that are positioned in upper and lower bands166 and 168. Third and fourth groups 170 and 172 of subcarriers,referred to as secondary and tertiary subcarriers respectively, are alsopositioned in upper and lower bands 166 and 168. Two referencesubcarriers 174 and 176 of the third group lie closest to the center ofthe channel. Subcarriers 178 and 180 can be used to transmit programinformation data.

FIG. 7 is a simplified functional block diagram of the relevantcomponents of an exemplary AM IBOC digital radio broadcasting receiver200. While only certain components of the receiver 200 are shown forexemplary purposes, it should be apparent that the receiver may comprisea number of additional components and may be distributed among a numberof separate enclosures having tuners and front-ends, speakers, remotecontrols, various input/output devices, etc. The receiver 200 has atuner 206 that includes an input 202 connected to an antenna 204. Thereceiver also includes a baseband processor 201 that includes a digitaldown converter 208 for producing a baseband signal on line 210. Ananalog demodulator 212 demodulates the analog modulated portion of thebaseband signal to produce an analog audio signal on line 214. A digitaldemodulator 216 demodulates the digitally modulated portion of thebaseband signal. Then the digital signal is deinterleaved by adeinterleaver 218, and decoded by a Viterbi decoder 220. A servicedemultiplexer 222 separates main and supplemental program signals fromdata signals. A processor 224 processes the program signals to produce adigital audio signal on line 226. The analog and main digital audiosignals are blended as shown in block 228, or a supplemental digitalaudio signal is passed through, to produce an audio output on line 230.A data processor 232 processes the data signals and produces data outputsignals on lines 234, 236 and 238. The data lines 234, 236, and 238 maybe multiplexed together onto a suitable bus such as an inter-integratedcircuit (I²C), serial peripheral interface (SPI), universal asynchronousreceiver/transmitter (UART), or universal serial bus (USB). The datasignals can include, for example, SIS, MPS data, SPS data, and one ormore AAS.

The host controller 240 receives and processes the data signals (e.g.,the SIS, MPSD, SPSD, and AAS signals). The host controller 240 comprisesa microcontroller that is coupled to the display control unit (DCU) 242and memory module 244. Any suitable microcontroller could be used suchas an Atmel® AVR 8-bit reduced instruction set computer (RISC)microcontroller, an advanced RISC machine (ARM®) 32-bit microcontrolleror any other suitable microcontroller. Additionally, a portion or all ofthe functions of the host controller 240 could be performed in abaseband processor (e.g., the processor 224 and/or data processor 232).The DCU 242 comprises any suitable I/O processor that controls thedisplay, which may be any suitable visual display such as an LCD or LEDdisplay. In certain embodiments, the DCU 242 may also control user inputcomponents via touch-screen display. In certain embodiments the hostcontroller 240 may also control user input from a keyboard, dials, knobsor other suitable inputs. The memory module 244 may include any suitabledata storage medium such as RAM, Flash ROM (e.g., an SD memory card),and/or a hard disk drive. In certain embodiments, the memory module 244may be included in an external component that communicates with the hostcontroller 240 such as a remote control.

FIG. 8 is a simplified functional block diagram of the relevantcomponents of an exemplary FM IBOC digital radio broadcasting receiver250. While only certain components of the receiver 250 are shown forexemplary purposes, it should be apparent that the receiver may comprisea number of additional components and may be distributed among a numberof separate enclosures having tuners and front-ends, speakers, remotecontrols, various input/output devices, etc. The exemplary receiverincludes a tuner 256 that has an input 252 connected to an antenna 254.The receiver also includes a baseband processor 251. The IF signal fromthe tuner 256 is provided to an analog-to-digital converter and digitaldown converter 258 to produce a baseband signal at output 260 comprisinga series of complex signal samples. The signal samples are complex inthat each sample comprises a “real” component and an “imaginary”component. An analog demodulator 262 demodulates the analog modulatedportion of the baseband signal to produce an analog audio signal on line264. The digitally modulated portion of the sampled baseband signal isnext filtered by isolation filter 266, which has a pass-band frequencyresponse comprising the collective set of subcarriers f₁-f_(n) presentin the received OFDM signal. First adjacent canceller (FAC) 268suppresses the effects of a first-adjacent interferer. Complex signal269 is routed to the input of acquisition module 296, which acquires orrecovers OFDM symbol timing offset or error and carrier frequency offsetor error from the received OFDM symbols as represented in receivedcomplex signal 298. Acquisition module 296 develops a symbol timingoffset Δt and carrier frequency offset Δf, as well as status and controlinformation. The signal is then demodulated (block 272) to demodulatethe digitally modulated portion of the baseband signal. Then the digitalsignal is deinterleaved by a deinterleaver 274, and decoded by a Viterbidecoder 276. A service demultiplexer 278 separates main and supplementalprogram signals from data signals. A processor 280 processes the mainand supplemental program signals to produce a digital audio signal online 282 and MPSD/SPSD 281. The analog and main digital audio signalsare blended as shown in block 284, or the supplemental program signal ispassed through, to produce an audio output on line 286. A data processor288 processes the data signals and produces data output signals on lines290, 292 and 294. The data lines 290, 292 and 294 may be multiplexedtogether onto a suitable bus such as an I²C, SPI, UART, or USB. The datasignals can include, for example, SIS, MPS data, SPS data, and one ormore AAS.

The host controller 296 receives and processes the data signals (e.g.,SIS, MPS data, SPS data, and AAS). The host controller 296 comprises amicrocontroller that is coupled to the DCU 298 and memory module 300.Any suitable microcontroller could be used such as an Atmel® AVR 8-bitRISC microcontroller, an advanced RISC machine (ARM®) 32-bitmicrocontroller or any other suitable microcontroller. Additionally, aportion or all of the functions of the host controller 296 could beperformed in a baseband processor (e.g., the processor 280 and/or dataprocessor 288). The DCU 298 comprises any suitable I/O processor thatcontrols the display, which may be any suitable visual display such asan LCD or LED display. In certain embodiments, the DCU 298 may alsocontrol user input components via a touch-screen display. In certainembodiments the host controller 296 may also control user input from akeyboard, dials, knobs or other suitable inputs. The memory module 300may include any suitable data storage medium such as RAM, Flash ROM(e.g., an SD memory card), and/or a hard disk drive. In certainembodiments, the memory module 300 may be included in an externalcomponent that communicates with the host controller 296 such as aremote control.

In practice, many of the signal processing functions shown in thereceivers of FIGS. 7 and 8 can be implemented using one or moreintegrated circuits. For example, while in FIGS. 7 and 8 the signalprocessing block, host controller, DCU, and memory module are shown asseparate components, the functions of two or more of these componentscould be combined in a single processor (e.g., a System on a Chip(SoC)).

FIGS. 9 a and 9 b are diagrams of an IBOC digital radio broadcastinglogical protocol stack from the transmitter perspective. From thereceiver perspective, the logical stack will be traversed in theopposite direction. Most of the data being passed between the variousentities within the protocol stack are in the form of protocol dataunits (PDUs). A PDU is a structured data block that is produced by aspecific layer (or process within a layer) of the protocol stack. ThePDUs of a given layer may encapsulate PDUs from the next higher layer ofthe stack and/or include content data and protocol control informationoriginating in the layer (or process) itself. The PDUs generated by eachlayer (or process) in the transmitter protocol stack are inputs to acorresponding layer (or process) in the receiver protocol stack.

As shown in FIGS. 9 a and 9 b, there is a configuration administrator330, which is a system function that supplies configuration and controlinformation to the various entities within the protocol stack. Theconfiguration/control information can include user defined settings, aswell as information generated from within the system such as GPS timeand position. The service interfaces 331 represent the interfaces forall services. The service interface may be different for each of thevarious types of services. For example, for MPS audio and SPS audio, theservice interface may be an audio card. For MPS data and SPS data theinterfaces may be in the form of different APIs. For all other dataservices the interface is in the form of a single API. An audio encoder332 encodes both MPS audio and SPS audio to produce core (Stream 0) andoptional enhancement (Stream 1) streams of MPS and SPS audio encodedpackets, which are passed to audio transport 333. Audio encoder 332 alsorelays unused capacity status to other parts of the system, thusallowing the inclusion of opportunistic data. MPS and SPS data isprocessed by PSD transport 334 to produce MPS and SPS data PDUs, whichare passed to audio transport 333. Audio transport 333 receives encodedaudio packets and PSD PDUs and outputs bit streams containing bothcompressed audio and program service data. The SIS transport 335receives SIS data from the configuration administrator and generates SISPDUs. A SIS PDU can contain station identification and locationinformation, indications regarding provided audio and data services, aswell as absolute time and position correlated to GPS, as well as otherinformation conveyed by the station. The AAS data transport 336 receivesAAS data from the service interface, as well as opportunistic bandwidthdata from the audio transport, and generates AAS data PDUs, which can bebased on quality of service parameters. The transport and encodingfunctions are collectively referred to as Layer 4 of the protocol stackand the corresponding transport PDUs are referred to as Layer 4 PDUs orL4 PDUs. Layer 2, which is the channel multiplex layer, (337) receivestransport PDUs from the SIS transport, AAS data transport, and audiotransport, and formats them into Layer 2 PDUs. A Layer 2 PDU includesprotocol control information and a payload, which can be audio, data, ora combination of audio and data. Layer 2 PDUs are routed through thecorrect logical channels to Layer 1 (338), wherein a logical channel isa signal path that conducts L1 PDUs through Layer 1 with a specifiedgrade of service, and possibly mapped into a predefined collection ofsubcarriers.

Layer 1 data in an IBOC system can be considered to be temporallydivided into frames (e.g., modem frames). In typical HD Radioapplications, each modem frame has a frame duration (T_(f)) ofapproximately 1.486 seconds. It will be appreciated that in otherbroadcast applications, a frame may have different durations. Each modemframe includes an absolute layer 1 frame number (ALFN) in the SIS, whichis a sequential number assigned to every Layer 1 frame. This ALFNcorresponds to the broadcast starting time of a modem frame. The starttime of ALFN 0 was 00:00:00 Universal Coordinated Time (UTC) on Jan. 6,1980 and each subsequent ALFN is incremented by one from the previousALFN. Thus the present time can be calculated by multiplying the nextframe's ALFN with T_(f) and adding the total to the start time of ALFN0.

There are multiple Layer 1 logical channels based on service mode,wherein a service mode is a specific configuration of operatingparameters specifying throughput, performance level, and selectedlogical channels. The number of active Layer 1 logical channels and thecharacteristics defining them vary for each service mode. Statusinformation is also passed between Layer 2 and Layer 1. Layer 1 convertsthe PDUs from Layer 2 and system control information into an AM or FMIBOC digital radio broadcasting waveform for transmission. Layer 1processing can include scrambling, channel encoding, interleaving, OFDMsubcarrier mapping, and OFDM signal generation. The output of OFDMsignal generation is a complex, baseband, time domain pulse representingthe digital portion of an IBOC signal for a particular symbol. Discretesymbols are concatenated to form a continuous time domain waveform,which is modulated to create an IBOC waveform for transmission.

FIG. 10 shows a logical protocol stack from the receiver perspective. AnIBOC waveform is received by the physical layer, Layer 1 (560), whichdemodulates the signal and processes it to separate the signal intological channels. The number and kind of logical channels will depend onthe service mode, and may include logical channels P1-P4, Primary IBOCData Service Logical Channel (PIDS), S1-S5, and SIDS. Layer 1 producesL1 PDUs corresponding to the logical channels and sends the PDUs toLayer 2 (565), which demultiplexes the L1 PDUs to produce SIS PDUs, AASPDUs, and Stream 0 (core) audio PDUs and Stream 1 (optional enhanced)audio PDUs. The SIS PDUs are then processed by the SIS transport 570 toproduce SIS data, the AAS PDUs are processed by the AAS transport 575 toproduce AAS data, and the PSD PDUs are processed by the PSD transport580 to produce MPS data (MPSD) and any SPS data (SPSD). Encapsulated PSDdata may also be included in AAS PDUs, thus processed by the AAStransport processor 575 and delivered on line 577 to PSD transportprocessor 580 for further processing and producing MPSD or SPSD. The SISdata, AAS data, MPSD and SPSD are then sent to a user interface 585. TheSIS data, if requested by a user, can then be displayed. Likewise, MPSD,SPSD, and any text based or graphical AAS data can be displayed. TheStream 0 and Stream 1 PDUs are processed by Layer 4, comprised of audiotransport 590 and audio decoder 595. There may be up to N audiotransports corresponding to the number of programs received on the IBOCwaveform. Each audio transport produces encoded MPS packets or SPSpackets, corresponding to each of the received programs. Layer 4receives control information from the user interface, including commandssuch as to store or play programs, and information related to seek orscan for radio stations broadcasting an all-digital or hybrid IBOCsignal. Layer 4 also provides status information to the user interface.

The following describes an exemplary process for digital radio broadcasttransmission and reception of media content for synchronized renderingat a digital radio broadcast receiver in accordance with exemplaryembodiments. First, a general description of exemplary components andoperation of a digital radio broadcast transmitter and digital radiobroadcast receiver will be provided. Then exemplary embodiments of twotechniques for transmitting and receiving synchronized media contentwill be discussed. Finally, exemplary applications of the disclosedembodiments will be discussed. Note that in the following description,reference will be made simultaneously to components of both theexemplary AM IBOC receiver of FIG. 7 and the exemplary FM IBOC receiverof FIG. 8 since the operation of both is substantially similar forpurposes of the present disclosure. Thus, for example, the hostcontroller is referred to below as the host controller 240, 296.

An exemplary functional block diagram of the transmit-side components ofa digital radio broadcast system is illustrated in FIG. 11. As discussedabove, the functions illustrated in FIG. 11 can be performed in asuitable combination of the importer 18, the exporter 20, and a client700. These components can comprise a processing system that may includeone or more processing units that may be co-located or distributed andthat are configured (e.g., programmed with software and/or firmware) toperform the functionality described herein, wherein the processingsystem can be suitably coupled to any suitable memory (e.g., RAM, FlashROM, ROM, optical storage, magnetic storage, etc.). The importer 18communicates with a client application 700 via a request/response-typeapplication program interface (API) (i.e., the importer 18 requests datafrom the clients) to receive data content such as album art, image slideshows, scrolling text information, closed captioning, product purchaseinformation, and video. The client application 700 can be any suitableprogram that has access to the data content, such as via a database orfile directory, and that is configured to prepare and send the mediacontent to the importer 18 in response to the importer's requests.

As discussed above, the importer 18 prepares the data content andsecondary audio (if any) from a secondary audio source 702 for digitalradio broadcast transmission. It should be noted that data content fromthe client 700 travels through a first signal path in the importer 18and the secondary audio for the SPS travels through a second signal pathdifferent from the first in the importer 18. Specifically, data contentfrom the client 700 is received by an RLS encoder 704 as AAS data whereit is encapsulated as discussed above. The data content can beencapsulated using packet-streaming techniques (e.g., standard orvariable packets or LOT) or the byte-streaming technique. Once the datacontent is encapsulated by the RLS encoder 704, the RLS packets are sentto the AAS/SPS multiplexer 708 where they are multiplexed with anysecondary audio (e.g., time-division multiplexed). It should be notedthat data is typically encoded via the RLS protocol which is differentthan the protocol used to transport the audio (e.g., audio transport 333illustrated in FIG. 9 b), and is therefore asynchronous with the audio.Secondary audio from the secondary audio source 702 is digitally encodedto produce compressed SPSA audio frames by the audio encoder 706. Anysuitable audio encoder can be used such as an HDC encoder as developedby Coding Technologies of Dolby Laboratories, Inc., 999 Brannan Street,San Francisco, Calif. 94103-4938 USA; an Advanced Audio Coding (AAC)encoder; an MPEG-1 Audio Layer 3 (MP3) encoder; or a Windows Media Audio(WMA) encoder. The secondary audio source 702 may also include PSD suchas music title, artist, album name, etc., which is encoded as SPSD PDUs.The SPSD PDUs are passed from the secondary audio source 702 through theaudio encoder 706 to the RLS encoder 704. The RLS encoder thenencapsulates the SPSD PDUs and passes RLS frames back to the audioencoder 706. The audio encoder 706 combines the SPSA audio frames andthe RLS encoded SPSD (if any) into a single SPS PDU and outputs it tothe AAS/SPS multiplexer 708. The AAS/SPS multiplexer 708 then outputspackets to the exporter 20 via the importer-to-exporter (I2E) interface710.

The I2E interface 710 is a two-way handshake link that exists betweenthe importer 18 and the exporter 20 to request AAS/SPS frames for aspecific modem frame. The I2E interface is typically a TCP/IP connectionalthough it could be any other suitable type of communicationconnection. As part of the I2E interface, there is a configurable framebuffer in the exporter 20 that can be used to overcome poor networkperformance when a TCP connection is used. The I2E interface 710 outputsthe multiplexed AAS/SPS packets to the multiplexer 712 in the exporter20.

The main audio travels through a separate signal path from the secondaryaudio and the data content, and therefore incurs a delay through thedigital broadcast system that is distinct from both the data content andthe secondary audio. Specifically, the main audio content is input atthe exporter 20, while the data content and the secondary content areinput at the importer 18. The main audio is provided by the main audiosource 714, and is digitally encoded to produce compressed MPSA audioframes by the audio encoder 716. Any suitable audio encoder can be usedas described above. The main audio source 714 may also include PSD thatis encoded as MPSD PDUs. The MPSD PDUs are passed from the audio encoder716 to the RLS encoder 718, where they are encapsulated and sent back tothe audio encoder 716 as RLS frames. The MPSD and MPSA packets arecombined into a single MPS PDU and then sent to the multiplexer 712. ASIS module generates the SIS information, including calculating thecurrent ALFN, and sends the SIS PDUs to the multiplexer 712. Themultiplexer 712 multiplexes the MPS, SPS, AAS, and SIS to form a modemframe. The multiplexer 712 then outputs the modem frame via the STL link14 (described with reference to FIG. 1 above) to the exciter 56, whichproduces the IBOC digital radio broadcasting waveform.

As noted above, the AAS, SPS and MPS may all travel through differentsignal paths in the digital radio broadcast transmission system therebyincurring different delays. The AAS incurs typically fixed delays due toRLS encoding and multiplexing in the importer 18. The SPS incurs notonly the delays for encoding (which is different than the RLS encodingdelay for data as previously discussed) and multiplexing, but alsoanother typically fixed delay for audio encoding in the importer 18. Thedelay for the SPS typically requires approximately six (6) modem framesof buffering to account for processing time. Furthermore, the SPS andAAS both incur an additional configurable delay through the I2E linkthat is typically on the order of 20 modem frames. As noted above, theMPS signal path does not pass through the I2E link and typicallyrequires only approximately one (1) modem frame of buffering to accountfor processing time in the exporter 20. In addition, the portion of thedigital radio broadcast transmitter downstream of the exporter 20typically incurs an additional two (2) modem frames of delay due tobuffering and processing. While approximate delay times have beenprovided for exemplary purposes, it should be apparent that theseexamples in no way limit the scope of this disclosure or the claims.

Similarly, the MPS and SPS audio and the AAS may travel throughdifferent signal paths in the digital radio broadcast receiver.Specifically, as discussed with reference to FIGS. 7 and 8, the MPS andSPS are decoded and output directly from the baseband processor 201, 251to the audio output 230, 286, whereas the AAS is transmitted as datacontent to the host controller 240, 296, from which it can be renderedvia the display control unit 242, 298. The digital radio broadcastreceiver typically incurs an approximately two (2) modem frames of delaydue to buffering and processing.

While it has been noted that the delays will typically vary from oneservice to another, it should also be noted that there may be differentdelays from one radio frequency to another, and from one geographiclocation to another. For example, since different radio stations mayemploy different hardware, software and/or configurations, the delaysthrough the systems due to processing and buffering will not be thesame.

As a result of these varying delays due to the multiple signal paths,audio and data content can incur different latencies through the digitalradio broadcast system. The digital radio broadcast transmitter accountsfor these different latencies so as to render audio and data content insynchronization at the digital radio broadcast receiver. The importer 18includes a delay determination module 722 that calculates approximatevalues for the various delays of data and audio through the signal pathsin the digital radio broadcast system and outputs these values to theclient 700. The delay determination module 722 can be implemented inhardware, software, or any suitable combination thereof (e.g., aprogrammed processing system).

The delay determination module 722 in conjunction with the client 700determine how far in advance of the start of a given piece of mediacontent (e.g., an audio track) another piece of media content (e.g., analbum art image) must be transmitted such that it is available forrendering at the receiver when the first piece of content arrives. Thefollowing variables are used to make this determination:

T₀=Current ALFN

D_(M)=MPS delay (ALFNs)

D_(S)=SPS delay (ALFNs)

D_(D)=Data delay (ALFNs)

T_(T)=Transfer Time of Media Content

S_(I)=Size of Media Content

B=Bandwidth allocated to the service in Bytes/PDU

R=Channel rate in PDU/sec

C=Conversion factor between ALFNs and seconds (e.g., 1.486 sec/ALFN)

The times are expressed in terms of ALFNs or fractions thereof forexemplary purposes, but also may be expressed in terms of units of timesuch as seconds, milliseconds, or any other suitable units.

To determine the audio latency D_(M) and D_(S), for MPS and SPS audiorespectively, the delay determination module 722 adds the various delaysincluding the I2E delay, the audio buffering delay, and thetransmit/receive delays. Similarly, to determine the data content delayD_(D), the delay determination module 722 adds the various delaysincluding the I2E delay, the data buffering delay, and thetransmit/receive delays. In exemplary embodiments, the delaydetermination module 722 receives the current ALFN (T₀) (i.e., the ALFNfor the modem frame currently being generated by the exporter 20) fromthe SIS module 720. The start of an audio segment will be delivered atthe Exciter (if MPS audio) or Importer (if SPS audio) at ALFN T_(A). Thelatency values can then be used to calculate a time T_(RENDER) at whichthe audio T_(A) or data content T_(D) delivered to the importer 18 is tobe rendered at the digital radio broadcast receiver by adding T₀ to thecalculated latency.

It should be noted that D_(D), i.e., the data delay, is typicallyavailable only if the data is being transmitted via standard packet modeor byte-streaming mode as discussed above. Typically, delays in othermodes (e.g., LOT and variable packet mode) are difficult to predictbecause the importer 18 does not know whether any individual packet ofdata will be transmitted in a given modem frame.

Next, the delay determination module 722 communicates T_(A), T_(D), andT₀ to the client 700. In certain embodiments, the delay determinationmodule 722 also sends channel data capacity information. This channeldata capacity typically includes the expected bandwidth allocated to theclient application B (e.g., a number of bytes that the channel cantransfer per frame), and the channel rate R (e.g., the number of framesper second). Using these two values, the client can determine thechannel capacity in bits-per-second. Given these values the clientapplication 700 can apply the proper timing either in the delivery ofthe data content to the importer 18 or in the packaging of the datacontent with timing instructions such that satisfactory timesynchronization can be achieved at the receiver.

The client 700 can calculate the transfer time of the media content fileT_(T) in ALFNs, which is a function of the bandwidth B, channel rate R,and size of the media content file S_(I). T_(T) represents the number ofALFNs needed to transfer a complete image. An exemplary calculation isas follows:

$T_{T} = \frac{S_{I}({bytes})}{{B\left( {{{bytes}/P}\; D\; U} \right)} \times {R\left( {P\; D\; {U/\sec}} \right)} \times {C\left( {{\sec/A}\; L\; F\; N} \right)}}$

Thus, to render the media content when the audio segment beginsrendering at the receiver, the client 700 determines the time T_(I) atwhich to start transferring the image file to the importer 18. T_(I) isa function of the transfer time T_(T), the delay of the audio throughthe system, and the delay of the data through the system. This may berepresented as: T_(I)=T_(A)−(T_(T)+(D_(D)−D_(M))) for MPS audio, andT_(I)=T_(A)−(T_(T)+(D_(D)−D_(S))) for SPS audio. FIG. 12 illustratesthis calculation.

In exemplary embodiments, the second media content arrives at thereceiver prior to the triggering instructions indicating that thereceiver should render the second media content. Second media contentsent too far in advance may not be stored in receiver memory at the timewhen it is needed for rendering and it may also be missed for receiverstuning from one station to another station. Preferably, the second mediacontent is sent less then 10 minutes in advance of its associatedtrigger. In some cases it may be desirable to make the media contentavailable in advance of the audio to guard against additional processingdelays or jitter associated with the data transport. And in someinstances, it may be desirable to retransmit the media contentimmediately after the beginning of the audio segment for example in casea user tunes to the audio service after it has started or the firstmedia content transmission was not received.

In cases where the completion of the media content is transmitted toarrive a short time before the audio content, the determination of thetransmit time could be represented asT_(I)=T_(A)+T_(G)−(T_(T)+(D_(D)−D_(M))), where T_(G) is a guard time.The guard time used will depend on various factors. First, it may dependon the chosen packet transport mechanism. For example, when usingstandard packet delivery mode or byte-streaming mode, every PDU willhave service data. In typical applications, a value of approximately 4-7frames was found to produce acceptable performance with standard packetdelivery mode. But when using variable packet delivery mode or LOT thebandwidth allocation is statistical in nature, depends on bandwidthallocated to other services using variable packet delivery mode or LOT,and there is no guaranteed time of delivery. As a result, guard timewill typically be larger when using these modes. As an example, incertain applications using variable packet delivery mode, an extra threeframes (approximately 5 seconds for P1 frames) may be added for a totalof 7 to 10 frames. As another example, if 500 bit/second are allocatedto a service, a LOT packet will only be transferred once every threeframes in exemplary embodiments. Accordingly, an extra three frames ofguard time may be added for a total of 7 to 10 frames. In addition, theguard time may depend on the speed and configuration of the receiver'shost processor. As will be appreciated, the determination of anappropriate guard time depends upon the implementation and may bedetermined empirically.

FIG. 13 illustrates an exemplary sequence of generating a modem frame inthe digital radio broadcast transmitter. Initially, the exporter 20sends a request message 740 to the importer 18 via the I2E interfacethat includes the current ALFN (N). This request message 740 notifiesthe importer 18 that the exporter is generating a modem frame identifiedby N and requests content for a logical channel. While described forexemplary purposes in terms of a single logical channel, it should bereadily apparent that the same process could apply to multiple logicalchannels generated for the current modem frame. The importer 18generates a content request message 742 for the client 700 that includesN, the audio ALFN, the data ALFN (if any), and the bandwidth and channelrate, which are determined as discussed above. In response, the client700 retrieves and sends data content 744 to the importer 18. Asdiscussed above, the client 700 applies the proper timing either in thedelivery of the data content to the importer 18 or in the packaging ofthe data content with timing instructions such that satisfactory timesynchronization can be achieved at the receiver. The importer 18generates data for a logical channel based on the content from theclient 700 and transmits this data 746 to the exporter 20 via the I2Einterface. The exporter 20 then generates and delivers modem frame N 748to the exciter 56 via the STL link 14 for digital radio broadcasttransmission 750. This process occurs within one modem frame time and isrepeated for each modem frame. Thus modem frame N+1 also shown in FIG.13 is generated and transmitted in the same manner.

There are several aspects to associating a client's data service with anaudio service: a) registering the data service with the importer 18; b)transmitting the association information to the receiver; and c)identification by the receiver that the data packets or LOT files areintended for a particular receiver application.

The registration of a data service with the importer is performed viathe importer API. This registration notifies the importer 18 that thedata service is to be associated with a given audio service and/orspecific audio program.

Once the data service is registered with the importer 18, data controlinstructions (e.g., SIG) are included in each modem frame that associatethe data content from the client 700 with the audio. These data controlinstructions cause the receiver to read the appropriate RLS port toaccess data content that is to be rendered in synchronization with theaudio. As discussed above, each modem frame typically includes a SIG.The SIG includes information regarding the data and audio services thatare advertised in SIS, including RLS port assignments. SIG allows thereceiver to determine that a service exists, pursue reception of theindicated service, and render the service if it is selected. However, itshould be noted that SIG does not necessarily provide access to thecontents of the service, for example, if the service is a CA service.SIG is broadcast over a fixed RLS port by the radio station thatprovides the service and is periodically updated.

Structurally, the SIG contains information pertaining to each servicebeing broadcast that is organized into service records. Typically, aseach client connects to the importer, a new audio or data service recordwill be constructed for that service. Service records typically includeinformation descriptors (i.e., attributes of the service). For example,an audio service record will typically include information thatdescribes the genre, additional processing instructions, and a servicedisplay name. In addition, a service may have other services associatedwith it. For example, an SPS may have data services associated with itas subservices that could include scrolling text, album art, closedcaptioning, product purchase information (e.g., ID3 tags), etc. In thiscase, the information about the associated subservice is included in theservice record of the main service. When a digital radio broadcastreceiver receives and decodes the SIG, it parses the information of theservice records to determine whether there are any associatedsubservices and renders any information about that subservice with thecurrent service. For example, if the receiver tunes to and renders SPS1,and the service record for SPS1 includes a subservice that includesalbum art, then the receiver will access the associated RLS portcontaining the album art.

An exemplary SIG message is illustrated in FIG. 14. The example in FIG.14 includes two concatenated service records, Service Record #1 andService Record #2. Service Record #1 describes an audio service (e.g.,SPS) and an associated data service. Service Record #1 includes a mainaudio service and a single associated data service, indicated by themain and subservice tags. The main service is an audio service andincludes audio service information descriptors. The subservice is anassociated data service (e.g., album art or closed captioninginformation) and includes data service information descriptors.Likewise, Service Record #2 describes only a main data service (e.g.,stock ticker or weather information). Service Record #2 includes a maindata service tag and data service information descriptors.

While the data content is described above as being associated with theaudio by including subservice information descriptors in the SIG, incertain embodiments the data content can be associated with the audio inother ways. For example, a descriptor of the main service could includea link to associate the audio service with a different data servicerecord.

After the digital radio broadcast transmitter broadcasts the modemframes over the air, a digital radio broadcast receiver then receivesthe modem frames and processes them so that the included content can berendered for an end user. The SIG and SIS MIME types and theirassociated hash values are used to identify that a particular datastream is associated with a particular receiver application (which mayor may not be available on the host processor of the receiver).Advantageously, a receiver may be able to receive programminginformation regarding stations that broadcast only in legacy analogwaveform and otherwise have no digital or other means of conveying theirprogram schedule.

As an example, a synchronized image application typically transmitsimages as an audio related data service using the LOT protocol totransmit images, although other data delivery modes such as standard andvariable packets and byte-streaming are possible. Each image may berepeated sufficiently to minimize loss of data due to bit errors asdescribed above.

In certain embodiments, a broadcaster may desire to or be required totransmit a textual promotional message along with an image, as mayhappen with an advertisement or images such as album art that arelicensed to the broadcaster for promotional use of the songs beingbroadcast. Also, it may be desirable to communicate to a listener alongwith an image that a song or other item or service may be purchased. Inthese cases, it may be desirable to require that the broadcaster alsotransmit a commercial frame in the PSD having a promotional message forthat particular song or album to show promotional use of the images.Because the promotional message is contained within PSD, it is alreadycoupled to its associated audio content and it can be broadcast at thesame time as the triggering information for its associated image. Otherimages such as artist/performance images, advertisements, local stationimages, program-related images, and genre-related images may also betransmitted. In these examples, a broadcaster may include supportingmessages in the commercial frame relating to the audio segment (e.g.,advertisements, talk shows) for which an image is being broadcast.Receivers may display the content of the commercial frame during therendering of the song/audio segment for which the image is beingbroadcast. These messages can be displayed at any time during theduration of the associated song/audio segment.

Text-based applications such as closed captioning, product purchaseinformation, or radio karaoke may transmit text using two differentmethods: 1) as an audio related data service using LOT, byte-streaming,or standard or variable packet delivery modes; or 2) in the ID3 tags ofthe PSD. In certain embodiments, LOT may be inefficient fortext-applications due to the typically small file size associated withtext and the large overhead for LOT encoding. Additionally, the jitterassociated with both LOT and variable packets may make these methodsinappropriate for real-time text applications such as closed captioning.Accordingly, for real-time text-based applications, such as closedcaptioning or radio karaoke, byte-streaming and standard packet modeswill be preferable because they provide guaranteed delivery times andminimal packet jitter. The text may be encoded using ASCII, ISO 8859-1,Unicode, or any other suitable method of text encoding as would be knownto one of skill in the art. Alternatively, text-based applications maytransmit text in the ID3 tags included with the PSD. For applicationsrequiring limited text such as providing product purchase information,including a commercial frame in the PSD may be preferable. However,since the capacity for extra text in the PSD may be limited, using aseparate data service may be preferable for other text-basedapplications.

The presentation time of media content is controlled by the serviceprovider at the transmitter side. This means that rendering the mediacontent associated with the audio service is done at the digital radiobroadcast receiver without the digital radio broadcast receiver makingdeterminations about the relative timing for rendering the second mediacontent and the first media content. This may be accomplished byincluding triggering instructions such as a custom ID3 frame with theother PSD information (e.g., song title, artist, tagging information,etc.) in an ID3 tag.

To synchronize the rendering of the media content with an audio program,the transmission of the triggering instructions is scheduled so thatthey arrive at the digital radio broadcast receiver to trigger immediaterendering of the media content in synchronization with the associatedaudio program. To accomplish this, the delay of the PSD relative to thevarious audio services is determined (e.g., based on empiricalmeasurements), and the ID3 frame with the control instructions isinserted into the relevant PSD. In order keep the PSD aligned with itsassociated audio, preferably within +/−3 seconds, PSD messages shouldarrive at the broadcast equipment within 0.5 seconds of each new audiosegment or song, and only one PSD message should be sent per audiosegment or song. If alignment tighter than +/−3 seconds is desired, thiscan be achieved using the measured values of PSD alignment to send ID3tags in advance of the audio. The delay of the PSD relative to the audioservices is based on the service mode, channel rate, and PSD size. Forexample, FIG. 15 shows that in certain embodiments a 100-byte PSDmessage arrives about two seconds before the associated MPS audio. FIG.15 also shows that a 550-byte PSD arrives approximately four secondsafter the MPS audio. It should be noted that SPS audio through theimporter incurs an additional audio buffering delay, and therefore thePSD for SPS audio arrives earlier than a similar PSD for MPS audio. Forexample, as shown in FIG. 16, a 550-byte PSD message arrives about 2.5seconds after the SPS audio.

The nominal PSD rate is approximately 125 bytes per frame for frame ratechannels. For block-pair rate channels, the nominal PSD rate isapproximately 7 bytes per block-pair (for MPS) and approximately 12bytes per block-pair (for SPS). Accordingly, each time the PSD sizesurpasses a 125-byte, 7-byte, or 12-byte multiple (for frame rate,block-pair rate MPS, and block-pair rate SPS respectively), the PSDtiming is altered by a frame (1.486 seconds) or a block-pair (0.185seconds). The determination of when to send the triggering instructionsso that the media content is triggered to render in synchronicity withthe audio program will take this additional delay into account.

In exemplary embodiments, the triggering instructions can take the formof a custom ID3 frame using experimental frame identifier “XHDR” totrigger immediate rendering of media content in synchronization with theaudio program. An exemplary format for the XHDR ID3 frame is shown inFIG. 17 and follows the ID3v2 specification, which is available athttp://www.id3.org and incorporated herein by reference in its entirety.The XHDR ID3 frame includes the following three parts:

1) ID3 frame header: This includes information regarding the size andcontent of the payload so that the receiver can determine whether it hassystem resources to decode and present the content.

2) MIME hash: The MIME hash field contains the MIME hash of theapplication sending the information.

3) Body: The body carries a list of different parameters describingactions to be performed by a receiver application.

As shown in FIG. 17, an exemplary ID3 frame header includes a frameIDthat consists of the four characters “XHDR,” a size field that containsthe frame size excluding the frame header, and a flag field for use asdescribed in the ID3v2 specification. An exemplary ID3 frame bodyincludes a list of different parameters followed by any specific dataneeded by that parameter. These parameters describe various actions tobe performed by the receiver application. For example, the display of animage transmitted via LOT can be triggered by the receipt of the “XHDR”frame that contains a LOTID that matches the LOTID of a received image.Similarly, if byte-streaming, standard packet, or variable packetdelivery modes are used, the “XHDR” frame could include a packetsequence number or range of packet sequence numbers that would triggerthe rendering of data in these packets (e.g., text data).

Table 3 below describes exemplary fields in the parameter definition:

TABLE 3 Parameter Description LOTID or The parameter instructs thereceiver to display the Sequence # image with the LOTID specified orrender the packet with the sequence # specified Flush The parameterinstructs the receiver application to Memory: clear its memory of allimages currently stored Blank The parameter instructs the receiverapplication to Display: blank the current display

In exemplary embodiments the client 700 can add a header to the datacontent to facilitate transport and decoding. FIG. 18 illustrates a datacontent packet in accordance with an exemplary content protocol. Thepacket includes an ordered collection of the following three items: aheader core 760, a header extension 762, and a body 764. The header core760 includes information regarding the size and the content of thepayload to enable a digital radio broadcast receiver to determinewhether it has system resources to decode and render the content. Theheader extension 762 includes information that supports the handling orrendering of the included content. And the body 764 carries the payload,where the structure and content of the data in the payload is describedin the header core 760 and the header extension 762.

The exemplary header core 760 is 8 bytes in length. While exemplarylengths are used herein for illustrative purposes, any suitable lengthsmay be used as would be readily apparent to one of ordinary skill in theart. The header core 760 includes a number of fields. First, there is aSYNC field, which is a two-byte ASCII sequence that identifies the startof the packet. These SYNC bytes can be used by the digital radiobroadcast receiver to defragment the packets when byte-streaming mode isused. Second, there is a one-byte PR field that describes the majorrevision (MAJ) and the minor revision (MIN) of the current protocolbeing used. This can be desirable to ensure that the receiver iscompatible with the protocol being used to encode the data content.Third, there is a one-byte Header EXT LEN field that describes thelength of the extension header in bytes. Fourth, there is a two-byteBody LEN field that describes the length of the body 764 in bytes. Incertain embodiments, a Body LEN of zero could indicate that the bodylength is greater than 2̂16 (65536) bytes and that there is a headerextension parameter describing the actual body length. Fifth, there is aone-byte Type field that indicates the type of data included in the body764. Finally, there is a one-byte Format field that indicates the formatof the data included in the body 764. Exemplary Type and Format valuesare shown in Table 4 below.

TABLE 4 Type Type Format Format Value Interpretation ValueInterpretation 0x0 PSD 0x0 XML 0x1 ID3 0x1 Audio 0x0 Uncompressed PCMsamples 0x1 HDC 0x2 Image 0x0 JPEG 0x1 PNG 0x2 GIF 0x3 Text 0x0 ISO/IEC8859-1:1998 0x4 ISO/IEC 10646-1:2000 0xff Other N/A Application specific

As illustrated in Table 4, the data content in the packets can includeXML, ID3 tags (for example as described in the ID3 informal standardversion 2.3.0 available at http://www.id3.org), uncompressed pulse codemodulated (PCM) audio samples, HDC encoded audio, JPEG images, PNGimages, GIF images, ISO/IEC 8859-1:1998 encoded text, ISO/IEC10646-1:2000 encoded text, or a form of data that is applicationspecific. While these data formats are shown for exemplary purposes,these examples in no way limit the scope of the disclosure or the claimsand any other form of data could be included as would be known to one ofordinary skill in the art such as, for example, MP3 audio, TIF images,MPEG-4 video, PDF or any other suitable data format.

The exemplary header extension 762 can be of variable length andincludes a number of parameters that describe various attributesassociated with the content. An exemplary list of parameters is shown inTable 5 below.

TABLE 5 Parameter Description StartALF: Specifies the time in ALFNs whenthe content is to be presented. If this value is 0 or absent the contentshould be presented immediately. EndALFN Specifies the time in ALFNswhen the content is no longer presented. If this value is 0 or absentthe content should be presented indefinitely until subsequent content isreceived. Duration Specifies the duration in ALFNs of contentpresentation. If this value is 0 or absent the content should bepresented indefinitely until subsequent content is received. BlockOffset Specifies the block offsets of the start and end ALFNs. The first4 bits represent the start offset and the next 4 bits represent the endoffset. ContentID A unique ID to identify or correlate a particularpiece of content. The structure of the ID is typically applicationspecific. Extended Indicates the body length in the number of bytes.Used in Body Length conjunction with a Body LEN of 0 in the header core.

As illustrated in Table 5, the header extension 762 can include startand end times, and durations for presenting content in the body 764.Additionally, the header extension can include a block offset thatallows the start and end content presentation times to be offset inincrements of 1/16 of the modem frame time (i.e., if the modem frametime is 1.48 seconds, then one block is 92.5 msecs in length). The blockoffset thereby allows fine-tuning of the synchronization of the datacontent with the audio to within approximately 92.5 msecs. Certainembodiments may provide a content reuse capability. For example, theextension header may include a Content ID descriptor that uniquelyidentifies the content described by the component. Receivers that havethe capability to store content can store the content referenced by theContent ID using the Content ID as an index. If in the future thereceiver identifies the same Content ID, instead of accessing thespecified RLS port to retrieve the content, the receiver can insteadretrieve the content from memory. This may be particularly advantageousfor content that is repetitive. For example, assume that a Top 40s radiostation broadcasts a limited number of songs. Therefore the receivercould store the album art associated with each of these songs and couldretrieve and display the album art as soon as each song begins.

An exemplary synchronized image application will now be described withreference to FIGS. 19 a to 19 d. In this application only a single image(e.g., an album cover) is displayed when triggered by the triggeringinstructions as shown in FIG. 19 a. Each image replaces the previousone, and remains on the display until it is in turn replaced. However,if a LOTID of an image is received in the triggering instructions (e.g.,XHDR ID3 frame) and the image cannot be located in receiver memory, incertain embodiments a default image may be displayed such as the stationlogo as shown in FIG. 19 b. If the default image is not available, thenthe current image may remain on the screen until a new valid LOTID isreceived, or the screen may display a blank image or a default HD Radiologo as shown in FIG. 19 c. In addition, certain applications may renderboth a station logo and album art as shown in FIG. 19 d.

The triggering instructions may also include memory managementinstructions for the receiver. For example, if a “Blank Display”Parameter ID as discussed above is received that is associated with thecurrently displayed image, then the image could be removed within fiveseconds. If a “Blank Display” Parameter ID is received that is notassociated with the currently displayed image, then it would not beremoved. Also, if a “Flush Memory” Parameter ID is received, then thereceiver memory would be purged of all previously stored images for theassociated service, with the possible exception of the station logo.Typically, upon receipt of a “Flush Memory” message, the receiver wouldalso remove the currently displayed image and display the station logountil the next image is received.

Default images or station logos are typically broadcast as a separateservice. These images are typically transmitted using LOT and should bestored in the receiver such that they will not be readily flushed frommemory. For example, the default image may continue to be stored evenafter tuning, whereas the other images should typically be flushed upontuning to a new channel. In exemplary embodiments, the LOTID associatedwith the default images should be unique from other images beingbroadcast via a synchronized image service. And when updating a defaultimage, the new default image should have a different LOTID from that ofthe old default image.

Upon receipt of an XHDR ID3 frame with the ParameterID of “1” (BlankDisplay), the image should be immediately removed from the display andnothing displayed until a new XHDR ID3 frame is received with a validLOTID. Upon receipt of the XHDR ID3 frame with the ParameterID set to“2) (Flush Memory), the receivers image memory should be flushed;removing all previously stored images except the default image. Thecurrent image may be immediately removed from the display and thedefault image should be displayed until a new LOTID is received with animage matching that LOTID that is available in the receiver's memory. Ifthe default image is not available, the image display may be blanked. Inthe event the synchronized image application is terminated, the screenshould return to the default image when it is restarted.

An exemplary process of receiving, processing, and rendering the datacontent is described below. First, the user powers on the digital radiobroadcast receiver and then tunes the receiver to a desired radiostation. On power-up, the host controller 240, 296 begins to repeatedlyrequest various types of data (e.g., SIS, SIG, and LOT segments) fromthe baseband processor 201, 251. The baseband processor 201, 251retrieves the SIS and SIG from the modem frame, decodes them, andcommunicates them to the host controller 240, 296 responsive to arequest. The host controller 240, 296 then parses the SIG record of thecurrently selected service to determine whether the station isbroadcasting any associated data content. This indication will typicallyinclude either identifying a component associated with the audiocomponent or a descriptor associating the audio component with anotherdata service. If associated data content is available on a particularstation, the SIG will also indicate the RLS port number on which theassociated data content can be received.

In certain embodiments the host controller may cause the display controlunit 242, 298 to render an indication to the user that associated datais available. For example, in closed captioning implementations thiscould be in the form of a lighted “Closed Captioning Available” buttonor an icon on a GUI. In certain embodiments, the user may be able tochoose whether to activate the closed captioning at this point. The usercan then activate the closed captioning, e.g., by pressing a suitablebutton, which can be for example, either a physical button on thereceiver or a soft key button on a GUI. In certain embodiments, the hostcontroller may automatically begin rendering available data contentwithout requiring user input.

While the receiver is tuned to a particular radio station, the basebandprocessor 250, 251 is continuously receiving and buffering RLS packetsthat are broadcast from the radio station. In embodiments directed topacket-mode transmission using LOT protocol, the data processor 232, 288may also be reassembling the packets into objects. These objects arethen passed to the host controller 240, 296 responsive to a request(e.g. a polling event). Alternatively, RLS packets could be passed tothe host controller 240, 296, which could then reassemble them intoobjects. Additionally, in embodiments directed to standard packets,variable packets, or byte-streaming data transmission, the RLS packetscould be reassembled in either the data processor 232, 288 or the hostcontroller 240, 296. The data content can then be reconstructed based onthe sequence numbers included in the packets as described above.

The host controller 240, 296 then renders and/or stores the reassembleddata content. The process of rendering and/or storing the data contentmay vary depending on the specific implementation and the receivercapabilities. For example, closed captioning information, radio karaoke,and streaming text may be rendered immediately in synchronization withthe audio (i.e., the synchronization is performed by the digital radiobroadcast transmitter and the receiver makes no determinations about therelative rendering timing of the data content) or the data content maybe temporarily or even momentarily stored until triggered by thetriggering instructions. Product purchase information included in thePSD such as a promotional message may be rendered immediately insynchronization with the associated audio track. Album art and imageslide shows will typically be stored for rendering in synchronizationwith the audio based on the triggering instructions included in an XHDRID3 frame identifying the image. In certain embodiments that allow forcontent reuse, the stored album art, image slide shows, and productpurchase information can be indexed with a content identifier so that itcan be accessed multiple times. The rendering applications can be codedin software using any suitable programming language such as C, C++, orfor example and implementing such applications is within the purview ofone of ordinary skill in the art.

Buffering images within the receiver memory, in general, may present abetter user experience to the listener. In order to meet the imagedisplay time requirements, the receiver may maintain a rendering bufferin memory to store the pre-sent synchronized images for the upcomingsongs within each multicast channel. Then, when the listener switches toa different multicast channel, the listener can be immediately presentedwith the primary image associated with the audio program.

The number of primary images buffered by the receiver for display can becontrolled by the baseband processor, specifically the internal LOTmemory pool within the baseband processor. However, for receivers wherethe internal baseband processor memory is less than 256 kb for LOT, thehost controller may need to account for additional buffering. In certainembodiments, receivers may store up to two primary images in their LOTmemory pool for all programs for the currently selected station.Assuming four programs, this would mean up to eight files of 24 kb eachfor a total of 192 kilobytes of storage. However, it is highly unlikelythat eight files will be the maximum size simultaneously, thus areasonable storage requirement is 144 kb (assuming an average file sizeof 18 kilobytes).

When the listener tunes away from the station, it may be desirable thatthe receiver flush all images associated with that station in order toconserve memory. If an image is fully received it may be desirable todiscard the image after a significant period of time has passed and notrigger has been received for the image. A timeout on the order of, forexample, 15 minutes may be desirable, although any other suitable timecould be used. However, discarding an image may only be done if there isinsufficient memory available to store a new image.

In typical embodiments, the station logos are repeated every 15 minutes,thus the receiver memory buffer should accommodate this. If the stationlogo cannot be found in the receiver memory, then the default imageshall be displayed if available or the display area shall be left blank.Each repetition of the station logo may be sent with the same LOT ID.The broadcaster will typically set the repeat value to a large number.They may also hold the LOT repeat value to the same non-zero value for alarge period of time across many repetitions until the image changes.They can then allow the repeat value to go to zero to indicate that thenext image is different. The next image will then have a different LOTID.

The station logos are typically read from LOT and stored in eitherreceiver memory. In typical embodiments, once a file is read from LOT,it is purged from the LOT memory pool and cannot be read again,therefore the receiver should maintain its own buffer of station logoimages. Once a station logo image has been read from the basebandprocessor LOT memory for a particular channel, it cannot be read again.For example, this scenario could occur in the case when a listener tunesto another channel and then chooses to tune back to the previouschannel. Thus, the station logos should be buffered (stored) in thereceiver host memory as soon as they are received and read from thebaseband processor. By doing this, the receiver will not have the needto download the station logos each time it is tuned to a differentmulticast program on the station. The receiver can also quickly revertto the station logo image when the synchronized image is not available.

In the worst-case scenario, where the listener first tunes to afour-program station and all images are being downloaded in LOTsimultaneously, this could mean a total of 12 images: 216 kb maximum(two primary images per program, current and next, and one station logoper program, and assuming an average file size of 18 kb). This mayapproach the total available memory space of LOT with the basebandprocessor. However, given the slow bit rate of the station logo images,the LOT memory pool will not be exceeded as long as the host controlleralways reads a station logo as soon as it is available and removes itfrom the LOT memory pool.

The memory buffer size for storing pending primary images shall bemanaged by flushing the images with the oldest discard time first. It ispreferable that the station logos be stored in non-volatile memory,cross-referenced by call sign and program number so that acquisitiontime is nominally very fast.

If the host controller were to store all the station logos for thecurrent market (broadcast region) in non-volatile memory, that wouldtotal four images per frequency (for four programs per frequency).Assuming 20 active frequencies transmitting the images, this totalmemory required would be: 18 kbytes×8×20=2.8 Mbytes (assuming a filesize of 18 kbytes)

The receiver may also choose to store the station logos in non-volatilememory for the available preset stations after the images have beendownloaded initially. This will enhance the user experience as well.There may also be cases where in order to make efficient use of theavailable memory pool, the host controller may disable the portsassociated with the primary image for all the other programs andmulticast channels except the current program/channel. In this use case,when switching to a different multicast program, the listener willinitially see the station logo for that channel and the receiver willdisplay the primary image only sometime after the start of the next songwhen it has downloaded and assembled the primary image for that song. Ifthe receiver chooses to adopt this method, it may be desirable that thereceiver does store the station logos for all programs on that station.

Synchronized images and station logos can be processed on the receiverentirely in the non-volatile or volatile memory available. Although afile system is not required on the receiver, a file system could bebeneficial for more efficient storage and retrieval of the image filesand memory management. This again may be governed by the receiver designand cost considerations.

Additionally, different receivers will have different input, display,and memory capabilities. Some typical receiver's displays may include 4line by 16 character LED or LCD displays, 2 line by 16 character LED orLCD displays, 256 color OEL displays, multi-line back lit LCD displayswith 6″ or larger multimedia displays, and portable radio back lit LCDdisplays. Generally the receivers with more advanced displays have moreavailable memory. Simpler receivers may only have a small amount of RAM(e.g., less than 50 Kbytes) while more advanced receivers may have alarger amount of RAM (e.g., 100 Kbytes or more) as well as non-volatilememory such as Flash ROM (e.g., built-in Flash, a hard disk drive,and/or a SD® Memory Card). Advantageously, exemplary embodiments of thepresent disclosure provide adaptable rendering and storage based on thecapabilities of the receiver.

The data content may be stored in any suitable memory structure. Forexample, a file system could be used such as NTFS or Journaling FlashFile System version 2 (JFFS2). Alternatively, the files could be storedin a database such as SQLite or MySQL. Naturally, the memory structureutilized should be consistent with the memory capabilities of thereceiver. Thus more capable receivers could have more complex memorystructures. In some embodiments the data content may be stored innon-volatile memory. In these cases, the data content may be availableimmediately upon power-up without requiring the download of any new datacontent.

The way the data content is rendered may also depend on the receivercharacteristics (e.g., display or memory capabilities) and/or accordingto user choice. For example, a simple embedded receiver may only receiveand display simple text-based data content while a more capable receivermay display, for example, image slide shows, album art, and even video.Once the data content has been formatted for the display, it can then berendered by the DCU 242, 298. In some embodiments filtering data contentmay be performed according to the end user's choice. Advantageously, thedisplayed data content may be reduced, for example, by preventingdisplay of album art or closed captioning, upon the end user's selectionand irrespective of the display's further capabilities.

Exemplary applications for synchronizing data content with audio contentwill now be described. The examples include an album art/image slideshow/video application, a closed captioning application, a productpurchase information application, and a scrolling text application.However, it should be understood that these examples are provided forillustrative purposes only and should not be considered to limit thescope of the disclosure or the claims.

An album art, an image slide show, and a video application would alltypically operate in a similar manner. As described above with referenceto FIGS. 11 and 13, the exporter 20 sends a request message to theimporter 18 for a logical channel to generate a modem frame. Part ofthis request is the ALFN of the current modem frame. The importer 18then makes a content request to the client application 700, whichrequest includes the current ALFN and the time at which the audiotransmitted in the modem frame is expected to be rendered by a digitalradio broadcast receiver. In this case, the client application 700 maybe, for example, an album art and/or an image slide show applicationthat includes an image repository containing, for example, JPG or GIFimages. The client application 700 also may be a video applicationincluding, for example, an H.264 video encoder, and a video repositorycontaining, for example, MPEG-4 video clips. The client application 700typically also has access to information related to the audio content.

The client application 700 schedules the transmission of the relevantimage and/or video for transmission such that the image and/or video isavailable at the receiver prior to the anticipated rendering time of therelated song. The nature of the scheduling algorithm is animplementation consideration that would be within the purview of one ofordinary skill in the art. Any suitable scheduling technique could beused that would allow the images/videos to arrive at the receiver intime for rendering with the associated audio. In certain embodiments, asophisticated scheduler could allow the image and/or video to arrive atthe receiver just in time for it to be rendered with the associatedaudio.

For example, a scheduling application could schedule rendering of one ormore images/videos associated with a song or audio program (e.g.,advertisement, sporting event, talk show, etc.) based on the start/endtimes of the song or audio program (or equivalently start time and songduration) and a duration percentage for displaying the images/video(i.e., how long each image is to be displayed with reference to theduration of the song or audio event). To obtain the song start/endtimes, the application could have access to a database that includes anaudio service's play list, wherein the database includes songsassociated with the time when each song will be input into the importer18 or exporter 20 for broadcast. To obtain a duration percentage foreach image/video, the image/video repository could include a displayorder and information describing a predetermined percentage of theassociated song. The scheduler would determine the appropriate times forrendering the images/videos based on this information and include thesetimes with the transmitted image/video.

FIG. 20 illustrates an exemplary image scheduling application operation.In the example, two songs are scheduled to be played. An audio play listdatabase indicates that Song 1 is scheduled to be sent to the exporter20 at time T_(i) and Song 2 is scheduled to be sent to the exporter 20at time T₃. Song 1 has two associated album art images (e.g., a frontalbum cover and a back album cover), while Song 2 has only one album artimage. The front album cover of the album is supposed to display for thefirst 70% of Song 1 while the back album cover is supposed to displayfor the last 30%. Given T₁ and the difference between T₀ and T_(A), theapplication determines the time, T_(Rx1), at which Song 1 will beginbeing rendered by a receiver (i.e., T_(Rx1)=T₁+(T_(A)−T₀)), and the timeT_(Rx3) at which Song 2 will begin being rendered by a receiver (i.e.,T_(Rx3)=T₃+(T_(A)−T₀)). The application then schedules rendering of thefront album cover at T_(Rx1) and the back album cover at time T_(Rx3).Similarly, based on a duration percentage of 30%, the applicationdetermines the time T_(Rx2) to begin displaying the back album cover.Triggering instructions scheduled to arrive at times T_(Rx1), T_(Rx2),and T_(Rx3) would then be transmitted identifying their respective albumart images.

The images and/or videos can be encoded using the LOT protocol and/orthe content protocol described above and sent in time to be availablefor rendering at the designated time. Triggering instructions (e.g., anXHDR ID3 frame) are then sent that, when executed, will cause thereceiver to immediately render the images/videos in synchronization withthe audio. Additionally, the SIG record for the service would indicatethat the receiver should use, for example, an album art or image slideshow application to render the data content by including appropriateMIME type identifiers. The client 700 sends the encoded images/videos tothe importer 18. The importer 18 then sends them to the exporter 20 fordigital radio broadcast transmission. While images and videos willtypically be encoded and transmitted using the LOT protocol, they mayalso be transmitted using standard packets, variable packets, orbyte-streaming. However, one of skill in the art would appreciate thatwhen images or videos are transmitted via these methods, availablebroadcast bandwidth may limit the size of images/videos. For example,larger images and videos typically take longer to transmit assuming afixed bandwidth availability. Therefore, assuming that the images/videosare transmitted so that they arrive just in time for rendering at thereceiver, the bandwidth constraints may limit the use of these methodsto images or videos that can be broadcast within, for example, theduration of a song, so that the image/video is available for renderingat the beginning of the next song.

In operation, the receiver will receive and download and store theimages and/or videos. When the triggering instructions indicate that theimage or video should be displayed (e.g., XHDR ID3 frame's LOTID matchesthe LOTID of the stored image), the image/video will be displayed by thedisplay control unit in synchronization with the receiver rendering theaudio via the audio speakers. In certain embodiments, if no images areavailable the receiver can display a default image.

A closed captioning application would provide text information that issynchronized with the audio. Examples of such an application can includeradio for the hearing impaired or language translations. In this case,the client application 700 is a closed captioning application. Forexample, the client 700 could receive closed captioning input from ahuman operator, a software implemented speech-to-text translator, or apre-stored text file containing the text of the speech that hasassociated rendering times for components of the speech. For a humanoperator, the client could present a word processing screen to theoperator that presents the text that has been typed and indicating whichtext has already been transmitted. For example, the words that have beentransmitted could be grayed out after they have been sent based on thecontent request messages received from the importer 18.

The text would be encoded as described above (e.g., using ISO 8859-1text in packets with sequence number identifiers). The sequence numbersof the packets allow the receiver to reassemble the text packets, andthe packets can be delimited using a fixed time or a predeterminednumber of characters (e.g., for standard packet mode). In certainembodiments, the text may be rendered by the receiver as soon as it isreceived. However, in certain embodiments the triggering instructionscan include sequence numbers that will cause the receiver to render thetext in synchronization with the audio. Additionally, the SIG wouldindicate that the receiver should use a text rendering application torender the data content by including an appropriate MIME typeidentifier.

Typically, the client 700 sends the text packets to the importer 18 sothat they arrive at the receiver just in time to be rendered insynchronization with the associated audio. Accordingly, this applicationwould typically use standard packets or byte-streaming to minimizedelivery jitter. Additionally, in certain embodiments the I2E link delaymay be reduced to minimize latency. In certain embodiments, the textpackets can be buffered by the client 700 to account for system latency.For example, the client 700 can use T_(A), T_(D), and T₀ to determinehow much to buffer the text packets so that the text is rendered insynchronization with the audio. In certain embodiments, the client 700can also use T_(A), T_(D), and T₀ to buffer the audio by providing aninput to the audio encoder, such that there is sufficient time for thetext to be generated and delivered to the importer 18.

In operation, the receiver may receive and immediately render the textcharacters. Alternatively, the text can be rendered in synchronizationwith the audio based on triggering instructions as described above. Thedisplay can be updated periodically as text is received (e.g., reset orlines of text scrolled up or down in a text box). For example, thereceiver could establish an average number of words per minute orcharacters per second so that the words would be rendered smoothly tomitigate the burstiness of delivery. Additionally, the display could beupdated upon receipt of a new text packet, after a predetermined amountof time, or when the text box on the display is full.

A radio karaoke application would also provide highly synchronized textwith the audio and would operate very similarly to the exemplary closedcaptioning application described above. However, in certain embodimentsa radio karaoke implementation may also include a receiver capabilityfor reducing and/or eliminating the vocals from an audio track in realtime. This may be desirable to improve the karaoke experience for users.FIGS. 21 a and 21 b illustrate exemplary components for receivercomponents in accordance with certain embodiments. FIG. 21 a illustratesan exemplary digital technique for reducing and/or eliminating the vocalcomponents of an audio track. With reference to FIGS. 7 and 8, theprocessor 224, 280 and blocks 230, 284 of an exemplary digital radiobroadcast receiver are shown. The audio signal from blocks 230, 284enters the vocal eliminator and audio processing block 770 where it isprocessed. The vocal eliminator and audio processing block 770 can beimplemented, for example, in the baseband processor 201, 251 or in aseparate processing system that includes software, hardware, or anysuitable combination thereof; and performs digital signal processingoperations on the audio sufficient to substantially filter out the vocalcomponent.

Any suitable vocal elimination algorithm could be used as would be knownto one of skill in the art. For example, assuming that the vocals areencoded on a center channel an exemplary algorithm might be as follows.The processing system could transform the left and right channels of theaudio signal to the frequency domain using, for example, the FastFourier Transform (FFT) or Fast Hartley Transform (FHT). Then, for eachfrequency component, where L is the 2D vector from the left channel, andR is the 2D vector from the right channel, the processing system wouldcompute the center component C=L/|L|+R/|R| and then compute α such that(L−αC)·(R−αC)=0. Essentially, the processing system would scale C sothat when it is subtracted from L and R, the two resultant vectors areperpendicular. Expanding this gives the equation(C·C)α²−C·(L+R)α+(L·R)=0, which the processing system may solve for α,for example, by the quadratic formula. Then, it would compute C′=αC,L′=L−αC, and R′=R−αC. Finally, it would transform L′, R′, and C′ back totime domain using an inverse FFT or FHT, overlap and add the signalcomponents back together. While this exemplary algorithm may result inan undesirable removal of low frequency components, a low pass filtercould also be used to extract and then reinsert these low frequencycomponents after the center component has been removed.

The vocal eliminator and audio processing block 770 also includes acontrol signal input that may, among other functions, activate anddeactivate the vocal eliminator operation. This control signal may begenerated by the host controller 240, 296 according to a user's input.For example, if a user is using a radio karaoke application, the usermay be presented with an icon or menu selection that allows them tochoose to eliminate the vocals (e.g., a “VOCAL ELIMINATOR” button).After processing the audio signal is then output to a digital-to-analogconverter 772 (DAC), which converts the digital signal to an analogaudio output suitable for rendering by, for example, analog speakers.

FIG. 21 b illustrates an exemplary analog technique for reducing and/oreliminating the vocal components of an audio track. The analog techniqueis similar to the digital technique except that the vocal eliminator andaudio processing block 774 is implemented after the DAC 772 andtypically would use electronic components such as, for example, adifferential amplifier for reducing the vocals and a low pass filter formaintaining the low frequency components.

In certain embodiments, the receiver may also provide the capability forrecording and storing a user's karaoke performance. For example, in areceiver including a microphone input and sufficient data storage (e.g.,a hard disk drive, flash ROM, and/or removable memory storage such as anSD card), a karaoke application at the receiver could allow a user toactivate a recording function. Once the recording function is activated,the user's vocals and the audio track, with or without the vocalsfiltered, could be mixed and stored in memory. The mixed audio could bestored, for example, in HDC compressed format and could be replayed at alater time. Exemplary storing and replaying functions in digital radiobroadcast receivers are disclosed in U.S. patent application Ser. No.11/644,083 (U.S. Patent Pub. No. 2008/0152039), which is incorporated byreference herein in its entirety.

A product purchase information application could send ID3 based productinformation as a commercial frame in the PSD, which is rendered insynchronization with associated songs. In exemplary embodiments the PSD(i.e., MPSD or SPSD) may include a commercial ID3 frame. This commercialframe can be used to facilitate the sale of products or services. It caninclude descriptive text that is typically a short promotional message(e.g., less than 128 bytes) as well as information such as the contactURL, name of seller, and price. The content of the commercial frame canbe populated by the broadcaster and/or service provider.

An exemplary commercial frame in ID3 format is shown below in Table 6.In exemplary embodiments, all the fields below are optional except theDescription field.

Field Name Format Text encoding One byte, where a value of 0x00 wouldindicate ISO/IEC 8859-1:1998 Price string A null-terminated text string,may include one three-character currency code, encoded according to ISO4217 alphabetic currency code, followed by a numerical value where “.”Is used a decimal separator. For example, in the U.S., the currency codeis “USD” Valid until Eight-character date string in the format YYYYMMDDContact URL Null-terminated text string Received as One byte describingwhether the commercial frame is associated with an image (e.g., albumart) Name of seller Null-terminated text string according to theencoding byte Description Null-terminated text string that is populatedwith a promotional message or advertisement text.

FIG. 19 a illustrates an exemplary application using the commercialframe. In this example, the receiver displays both a promotional messagecontained in a commercial frame and the album art associated with theaudio track currently being rendered. As shown, the promotional messageis “This song is available for sale online!” Any other suitablepromotional messages can be included such as “This song is available forpurchase on iTunes®,” or “This song is available for instant download onAmazon.com®.”

In alternative embodiments, the commercial frame may be included as aseparate data service using standard packets, variable packets, LOTprotocol, or byte-streaming. Since text-based commercial informationwill typically not be very large, it may readily be sent using standardpackets, variable packets, or byte-streaming. On the other hand, imageor video based product purchase information will more readily be sentusing LOT protocol. In these embodiments, the SIG record for the servicewould indicate that the receiver should use a product purchaseinformation application to render the data content by including anappropriate MIME type identifier. Further, the client 700 could use therendering start and stop times as validity times to match the productpurchase information with the specific content being rendered. On thereceiver side, once the user of the receiver inputs instructions topurchase a product associated with the current media content (e.g.,presses a tagging button), the application can poll the current ALFNfrom the SIS and match this ALFN to the proper product information. Thisproduct purchase information can then be transmitted to a contentprovider to consummate a sale. A detailed example of tagging for digitalradio broadcast receivers can be found in U.S. Patent App. Pub. No.2009/0061763, which is incorporated by reference herein in its entirety.Client applications for sending PSD information (e.g., ID3 tags)associated with the audio could operate in a similar manner.

Finally, a scrolling text application is an informational textapplication wherein the text is not as tightly coupled to the audio asin the closed captioning application. Examples of scrolling textapplications can include stock quotes, traffic advisories, etc. Theoperation of a scrolling text application is almost identical to that ofa closed captioning application. However, triggering instructionstypically need not be provided and the level of synchronization betweenthe audio and the text packets need not be very high. For example, therewould be little need to buffer the audio to account for text generationtime or to reduce the I2E link delay time. For these applications, theSIG would indicate that the receiver should use a scrolling textapplication to render the data content by including an appropriate MIMEtype identifier. In certain embodiments, if no new text packets areavailable at the receiver, then the receiver will scroll the last textpacket until a new one is received.

FIG. 22 illustrates an exemplary process of encoding and transmitting afirst media content (e.g., audio), a second media content (e.g., datacontent), and triggering instructions (e.g., an XHDR ID3 frame with thePSD) in a digital radio broadcast system comprising a processing system.The process is characterized by the fact that the triggeringinstructions arrive to trigger immediate rendering (i.e., as soon aspracticable without purposeful delay) of the second media content insynchronization with the first media content by a digital radiobroadcast receiver. In step 800, the importer 18 determines a firstvalue (T₀) corresponding to a time at which a frame is to be transmittedby a digital radio broadcast transmitter.

In step 802, the importer 18 determines a second value (T_(A))corresponding to a time at which a first media content transmitted inthe frame is to be rendered by a digital radio broadcast receiver basedon a first latency, wherein the first media content is processed througha first signal path through the digital radio broadcast transmitterthereby incurring a first latency that is based on an estimated time forprocessing the first media content through the first signal path. Forexample, referring to FIG. 11, main audio is output from the main audiosource 714 to the audio encoder 716 in the exporter 20 and then tomultiplexer 712. In contrast, secondary audio is output from thesecondary audio source 702 to the audio encoder 706, then throughmultiplexer 708 and finally to the exporter multiplexer 712 via I2Einterface 710. Accordingly, it should be clear from this example thatmain audio and secondary audio would typically incur different latenciesthrough the transmitter side.

In step 804, the importer determines a third value (T_(D)) correspondingto a time at which a second media content in the frame would be renderedby the digital radio broadcast receiver based on a second latency,wherein the second media content is processed through a second signalpath through the digital radio broadcast transmitter thereby incurringthe second latency that is based on an estimated time for processing thefirst media content through the first signal path. This second latencyis typically different than the first latency. For example, referringagain to FIG. 11, data content is output from the client 700 to the RLSencoder 704, then through multiplexer 708 and finally to the exportermultiplexer 712 via I2E interface 710. Thus it should be apparent thatthe latency of data content will typically be different than the latencyof audio content through the transmitter side.

In step 806, the importer 18 determines the channel data capacity. Thischannel data capacity is based on the allocated bandwidth and thechannel rate.

In step 808, the importer 18 communicates the first, second, and thirdvalues and the channel data capacity to a client application 700 via anAPI. The client application 700 may be, for example, a closed captioningapplication, a karaoke radio application, a scrolling text application,album art, or a product purchase information application. The clientapplication 700 then processes the second media content at a timedetermined by the client 700 based on the first, second, and thirdvalues and the channel data capacity to determine a time at which secondmedia content is to be transmitted to the digital radio broadcastreceiver. This is performed so as to synchronize the timing of renderingthe second media content at a digital radio broadcast receiver relativeto the timing of rendering of the first media content at the digitalradio broadcast receiver.

In step 810, the client 700 generates triggering instructions forinsertion into the PSD based on the first, second, and third value andthe channel data capacity. These triggering instructions will triggerthe rendering of the second media content in synchronization with thefirst media content at the receiver. These triggering instructions aretransmitted such that they arrive at the receiver to trigger immediaterendering of the second media content in synchronization with the firstmedia content. In other words, the triggering instructions are executedby the receiver immediately upon receipt as opposed to being stored forlater implementation.

Finally, in step 812 the importer 18 communicates the second mediacontent and triggering instructions to the exporter 20. In turn, theexporter 20 communicates the second media content, triggeringinstructions, and first value (i.e., T₀) to a digital radio broadcasttransmitter site via STL link 14 for digital radio broadcast.

In certain embodiments, the first latency and the second latency aretransmission-location dependent meaning that the latencies can vary fromradio station to radio station and from one service to another. Incertain embodiments, the digital radio broadcast receiver renders thefirst media content and second media content without makingdeterminations about the relative rendering timing for the second mediacontent and the first media content. In certain embodiments, the framedoes not include an independent clock signal for synchronizing the firstand second media content.

FIG. 23 illustrates an exemplary process of processing first mediacontent, second media content and triggering instructions received viadigital radio broadcast transmission such that the triggeringinstructions arrive for immediate execution to trigger immediaterendering of the second media content in synchronization with the firstmedia content.

In step 840, the baseband processor 201, 251 receives a frame havingfirst media content (e.g., audio) and second media content (e.g., datacontent such as audio, radio karaoke, or closed captioning). The secondmedia content has been composed for rendering in synchronization withthe first media content based on an estimated latency through thedigital radio broadcast transmitter and the digital radio broadcastreceiver as discussed above.

In step 842, the baseband processor 201, 251 also receives triggeringinstructions (e.g., an XHDR ID3 frame with the PSD) and data controlinstructions (e.g., SIG) associating the second media content with thefirst media content. These triggering instructions and data controlinstructions are typically included in the PSD. The triggeringinstructions are configured to cause the second media content to berendered by a digital radio broadcast receiver based on the time atwhich the first media content will be rendered, and are scheduled at thetransmitter side so as to arrive at the digital radio broadcast receiverfor immediate execution to trigger immediate rendering of the secondmedia content in synchronization with the first media content.

In step 844, the baseband processor 201, 251 begins rendering the firstmedia content via, for example, the speakers. In step 846, the basebandprocessor determines whether a commercial frame having a promotionalmessage associated with the second media content has also been received.In exemplary embodiments, the commercial frame will be included in thePSD. If so, then in step 848, then the baseband processor 201, 251renders the second media content and the promotional message from thecommercial frame in synchronization with the first media content. Forexample, this promotional message may be displayed at any time duringthe display of the second media content. However, if the commercialframe having the promotional message associated with the second mediacontent has not been received, then in step 850 the baseband processor201, 251 refrains from rendering the second media content.

In certain embodiments, the triggering instructions may include memorymanagement instructions. For example, they may include instructions forcausing the digital radio broadcast receiver to flush a memory, e.g., a“Flush Memory” Parameter ID as described above. Or they may includeinstructions for causing the digital radio broadcast receiver to blank adisplay such as the “Blank Display” Parameter ID described above.

The triggering instructions are composed such that they arrive forimmediate execution to trigger immediate rendering of the second mediacontent in synchronization with the first media content. In other words,the digital radio broadcast receiver renders the first media content andsecond media content without making determinations about the relativerendering timing for the second media content and the first mediacontent. In certain embodiments, the frame does not include anindependent clock signal for synchronizing the first and second mediacontent. The second media content may include, for example, closedcaptioning information, song lyrics, album art, image slide shows,product purchase information, or scrolling text. In certain embodimentsthe second media content can be radio karaoke information (e.g., songlyrics) and the receiver can filter vocal components of the audio inreal time so as to reduce the vocal component as described above withreference to FIGS. 20 a and 20 b.

The previously described embodiments of the present disclosure have manyadvantages, including:

One advantage is that in certain embodiments, audio and data content canbe rendered in synchronization at the receiver without transmitting anindependent clock reference to the receiver that could be referenced forboth audio and data rendering. Thus there are no significantmodifications to the baseband processor required. Additionally,including an additional clock signal would require additional bandwidth,which is at a premium in digital radio broadcast systems.

Another advantage is that in certain embodiments, audio and data contentcan be rendered in synchronization at the receiver without referencingthe rendering of data content to the playback of the audio. Thus nosignificant changes to the baseband processor would be required.

An advantage is that in certain embodiments the second media content(e.g., album art) may be stored for the shortest possible time sincesuch content is transmitted so as to be received just prior to beingrendered (e.g., up to 10 frames before the audio content). This has thebenefit of minimizing the overall time that the second content (e.g.,album art) needs to be stored, and as such also reduces the overallstorage capacity needed for the second content since different instancesof second content (e.g., album art images for other audio tracks) neednot be simultaneously stored.

The exemplary approaches described may be carried out using any suitablecombinations of software, firmware and hardware and are not limited toany particular combinations of such. Computer program instructions forimplementing the exemplary approaches described herein may be embodiedon a computer-readable storage medium, such as a magnetic disk or othermagnetic memory, an optical disk (e.g., DVD) or other optical memory,RAM, ROM, or any other suitable memory such as Flash memory, memorycards, etc. Additionally, the disclosure has been described withreference to particular embodiments. However, it will be readilyapparent to those skilled in the art that it is possible to embody thedisclosure in specific forms other than those of the embodimentsdescribed above. The embodiments are merely illustrative and should notbe considered restrictive. The scope of the disclosure is given by theappended claims, rather than the preceding description, and allvariations and equivalents which fall within the range of the claims areintended to be embraced therein.

1. A digital radio broadcast transmitter system configured to encode andtransmit first media content, second media content and triggeringinstructions to a digital radio broadcast receiver such that thetriggering instructions arrive for immediate execution to triggerimmediate rendering of the second media content in synchronization withthe first media content, comprising: a processing system; and a memorycoupled to the processing system, wherein the processing system isconfigured to execute steps comprising: determining at the processingsystem a first value corresponding to a time at which a frame includingfirst media content is to be transmitted by a digital radio broadcasttransmitter; determining at the processing system a second valuecorresponding to a time at which first media content transmitted in theframe is to be rendered by a digital radio broadcast receiver based on afirst latency, wherein the first latency is based on an estimated timefor processing the first media content via a first signal path throughthe digital radio broadcast transmitter; determining at the processingsystem a third value corresponding to a time at which second mediacontent would be rendered by the digital radio broadcast receiver basedon a second latency, wherein the second latency is based on an estimatedtime for processing the second media content via a second signal paththrough the digital radio broadcast transmitter, and wherein the secondlatency is different than the first latency; determining at theprocessing system a channel data capacity for broadcasting the secondmedia content via digital radio broadcast transmission; processing thesecond media content at the processing system based on the first value,second value, third value and the channel data capacity to determine atime at which second media content is to be transmitted to the digitalradio broadcast receiver, so as to be received at a digital broadcastradio receiver for rendering in synchronization with the first mediacontent at the digital radio broadcast receiver; generating triggeringinstructions based on the first value, second value, third value and thechannel data capacity to trigger the rendering of the second mediacontent in synchronization with the first media content at the digitalradio broadcast receiver, such that the triggering instructions arriveat the digital radio broadcast receiver for immediate execution totrigger immediate rendering of the second media content insynchronization with the first media content; and communicating to thedigital radio broadcast transmitter, the first value, first mediacontent, second media content, and the triggering instructions; whereinthe triggering instructions are transmitted in an ID3 frame with programservice data.
 2. The digital radio broadcast transmitter system of claim1 wherein the time at which second media content is to be transmitted tothe digital radio broadcast receiver is such that the second mediacontent arrives at the digital radio broadcast receiver at most 10frames before the triggering instructions arrive at the digital radiobroadcast receiver.
 3. The digital radio broadcast transmitter system ofclaim 1 wherein the first latency and the second latency depend upon ageographic location of the digital radio broadcast transmitter.
 4. Thedigital radio broadcast transmitter system of claim 1 comprisingrendering the first media content and second media content at thedigital radio broadcast receiver without the digital radio broadcastreceiver making determinations about the relative timing for renderingthe second media content and the first media content.
 5. The digitalradio broadcast transmitter system of claim 1 wherein the frame does notinclude an independent clock signal for synchronizing the first andsecond media content.
 6. The digital radio broadcast transmitter systemof claim 1 wherein the first media content is audio content.
 7. Thedigital radio broadcast transmitter system of claim 1 wherein the secondmedia content comprises closed captioning information.
 8. The digitalradio broadcast transmitter system of claim 1 wherein the second mediacontent comprises images.
 9. The digital radio broadcast transmittersystem of claim 1 wherein the second media content comprises productpurchase information configured to associate a current media contentbeing rendered with a product to be purchased corresponding to thesecond media content, such that a user of the digital radio broadcastreceiver can input instructions to purchase a product associated withthe current media content.
 10. The digital radio broadcast transmittersystem of claim 1 wherein processing the second media content at theprocessing system comprises: communicating the first, second, and thirdvalues and the channel data capacity to a client; and receiving secondmedia content for the frame from the client at a time at which secondmedia content is to be transmitted to the digital radio broadcastreceiver, so as to be received at a digital broadcast radio receiver forrendering in synchronization with the first media content at the digitalradio broadcast receiver.
 11. The digital radio broadcast transmittersystem of claim 1 wherein the triggering instructions includeinstructions for causing the digital radio broadcast receiver to flush amemory.
 12. The digital radio broadcast transmitter system of claim 1wherein the triggering instructions include instructions for causing thedigital radio broadcast receiver to blank a display.
 13. Acomputer-implemented method of encoding and transmitting first mediacontent, second media content and triggering instructions to a digitalradio broadcast receiver such that the triggering instructions arrivefor immediate execution to trigger immediate rendering of the secondmedia content in synchronization with the first media content, themethod comprising: determining at the processing system a first valuecorresponding to a time at which a frame including first media contentis to be transmitted by a digital radio broadcast transmitter;determining at the processing system a second value corresponding to atime at which first media content transmitted in the frame is to berendered by a digital radio broadcast receiver based on a first latency,wherein the first latency is based on an estimated time for processingthe first media content via a first signal path through the digitalradio broadcast transmitter; determining at the processing system athird value corresponding to a time at which second media content wouldbe rendered by the digital radio broadcast receiver based on a secondlatency, wherein the second latency is based on an estimated time forprocessing the second media content via a second signal path through thedigital radio broadcast transmitter, and wherein the second latency isdifferent than the first latency; determining at the processing system achannel data capacity for broadcasting the second media content viadigital radio broadcast transmission; processing the second mediacontent at the processing system based on the first value, second value,third value and the channel data capacity to determine a time at whichsecond media content is to be transmitted to the digital radio broadcastreceiver, so as to as to be received at a digital broadcast radioreceiver for rendering in synchronization with the first media contentat the digital radio broadcast receiver; generating triggeringinstructions based on the first value, second value, third value and thechannel data capacity to trigger the rendering of the second mediacontent in synchronization with the first media content at the digitalradio broadcast receiver, such that the triggering instructions arriveat the digital radio broadcast receiver for immediate execution totrigger immediate rendering of the second media content insynchronization with the first media content; and communicating to thedigital radio broadcast transmitter, the first value, first mediacontent, second media content, and the triggering instructions; whereinthe triggering instructions are transmitted in an ID3 frame with programservice data.
 14. The method of claim 13 wherein the time at whichsecond media content is to be transmitted to the digital radio broadcastreceiver is such that the second media content arrives at the digitalradio broadcast receiver at most 10 frames before the triggeringinstructions arrive at the digital radio broadcast receiver.
 15. Themethod of claim 13 wherein the first latency and the second latencydepend upon a geographic location of the digital radio broadcasttransmitter.
 16. The method of claim 13 comprising rendering the firstmedia content and second media content at the digital radio broadcastreceiver without the digital radio broadcast receiver makingdeterminations about the relative timing for rendering the second mediacontent and the first media content.
 17. The method of claim 13 whereinthe frame does not include an independent clock signal for synchronizingthe first and second media content.
 18. The method of claim 13 whereinthe first media content is audio content.
 19. The method of claim 13wherein the second media content comprises closed captioninginformation.
 20. The method of claim 13 wherein the second media contentcomprises images.
 21. The method of claim 13 wherein the second mediacontent comprises product purchase information configured to associate acurrent media content being rendered with a product to be purchasedcorresponding to the second media content, such that a user of a digitalradio broadcast receiver can input instructions to purchase a productassociated with the current media content.
 22. The method of claim 13wherein processing the second media content at the processing systemcomprises: communicating the first, second, and third values and thechannel data capacity to a client; and receiving second media contentfor the frame from the client at a time at which second media content isto be transmitted to the digital radio broadcast receiver, so as to bereceived at a digital broadcast radio receiver for rendering insynchronization with the first media content at the digital radiobroadcast receiver.
 23. The method of claim 13 wherein the triggeringinstructions include instructions for causing the digital radiobroadcast receiver to flush a memory.
 24. The method of claim 13 whereinthe triggering instructions include instructions for causing the digitalradio broadcast receiver to blank a display.
 25. An article ofmanufacture comprising a computer readable storage medium havingcomputer program instructions adapted to cause a processing system toexecute the steps of claim
 13. 26. A digital radio broadcast receiverfor processing first media content, second media content and triggeringinstructions received via digital radio broadcast transmission such thatthe triggering instructions arrive for immediate execution to triggerimmediate rendering of the second media content in synchronization withthe first media content, comprising: a processing system; and a memorycoupled to the processing system, wherein the processing system isconfigured to execute steps comprising: receiving first media contentand second media content; receiving triggering instructions to cause thesecond media content to be rendered by a digital radio broadcastreceiver based on the time at which the first media content will berendered, wherein the triggering instructions are scheduled so as toarrive at the digital radio broadcast receiver for immediate executionto trigger immediate rendering of the second media content insynchronization with the first media content; rendering the first mediacontent; determining whether a commercial frame having a promotionalmessage associated with the second media content has been received; andif the commercial frame having the promotional message associated withthe second media content has not been received, refraining fromrendering the second media content; wherein the triggering instructionsare received in an ID3 frame with program service data.
 27. The methodof claim 26 wherein the frame does not include an independent clocksignal for synchronizing the first and second media content.
 28. Themethod of claim 26 wherein the first media content is audio.
 29. Themethod of claim 26 wherein the second media content comprises images.30. The method of claim 26 wherein the triggering instructions includeinstructions for causing the digital radio broadcast receiver to flush amemory.
 31. The method of claim 26 wherein the triggering instructionsinclude instructions for causing the digital radio broadcast receiver toblank a display.
 32. An article of manufacture comprising a computerreadable storage medium having computer program instructions adapted tocause a processing system to execute the steps of claim
 26. 33. Adigital radio broadcast system for processing first media content,second media content and triggering instructions for broadcast to adigital radio broadcast receiver via digital radio broadcasttransmission such that the triggering instructions arrive for immediateexecution to trigger immediate rendering of the second media content insynchronization with the first media content, comprising: a processingsystem; and a memory coupled to the processing system, wherein theprocessing system is configured to execute steps comprising: determininga time at which a first media content will be rendered at a digitalradio broadcast receiver; generating triggering instructions to cause asecond media content to be rendered by a digital radio broadcastreceiver based on the time at which the first media content will berendered, wherein the triggering instructions are scheduled so as toarrive at the digital radio broadcast receiver for immediate executionto trigger immediate rendering of the second media content insynchronization with the first media content; processing broadcastframes including the first media content and the triggering instructionsfor broadcast via digital radio broadcast transmission; determiningwhether a commercial frame having a promotional message associated withthe second media content has been generated; and if the commercial framehas been generated, processing the second media content and thecommercial frame for broadcast via digital radio broadcast transmission,the commercial frame being timed for rendering at the digital radiobroadcast receiver along with the first media content and the secondmedia content; wherein the triggering instructions are transmitted in anID3 frame with program service data.
 34. A computer-implemented methodfor processing first media content, second media content and triggeringinstructions for broadcast to a digital radio broadcast receiver viadigital radio broadcast transmission such that the triggeringinstructions arrive for immediate execution to trigger immediaterendering of the second media content in synchronization with the firstmedia content, comprising: determining a time at which a first mediacontent will be rendered at a digital radio broadcast receiver;generating triggering instructions to cause a second media content to berendered by a digital radio broadcast receiver based on the time atwhich the first media content will be rendered, wherein the triggeringinstructions are scheduled so as to arrive at the digital radiobroadcast receiver for immediate execution to trigger immediaterendering of the second media content in synchronization with the firstmedia content; processing broadcast frames including the first mediacontent and the triggering instructions for broadcast via digital radiobroadcast transmission; determining whether a commercial frame having apromotional message associated with the second media content has beengenerated; and if the commercial frame has been generated, processingthe second media content and the commercial frame for broadcast viadigital radio broadcast transmission, the commercial frame being timedfor rendering at the digital radio broadcast receiver along with thefirst media content and the second media content; wherein the triggeringinstructions are received in an ID3 frame with program service data.